Migrating email service providers can be a large undertaking. We want to help relieve some of that stress of moving to Postmark from Amazon SES. This guide will detail some of the differences and similarities between SES and Postmark, as well as give some useful tips for migrating to Postmark from SES.
It includes details on differences between the Postmark and SES APIs, sending outbound emails, processing inbound emails, UI differences, and webhooks. For quick reference, we have included tables where possible to equate SES functionality and JSON fields to their comparable functionality and fields in Postmark.
Since Postmark does not allow bulk email (including subscription newsletters), there are no list management features available in Postmark, such as creating lists, handling unsubscribes, or adding unsubscribe links to your emails automatically.
You do not need to set up your own logging or perform any additional steps to store sent messages. Successfully sent messages are stored for 45 days in Postmark automatically (including the content and delivery events). Sent messages are available to view using our UI or you can pull them with our REST API.
Bounces and spam complaints are also stored indefinitely, for troubleshooting purposes.
Postmark's developer plan provides you with 100 emails per month. This is the only free plan and can be used for trying out our service.
Important concepts to learn when moving over to Postmark
There are a couple important concepts to learn when moving over to Postmark: Servers and Sender Signatures, and Verified Domains. A server and a confirmed sender signature/verified domain are required for sending, so it is important to understand what they are used for.
Each Postmark account contains servers. Servers can be thought of as folders you create that group together similar email activity. Each server has its own activity (inbound and outbound), stats, server API token(s), a unique inbound email address, and templates. You can create as many servers as you need, there is no limit.
Some uses of servers are separating your clients’ activity, sending emails for different environments (prod, staging, development), or separating sending for your different domains. When you begin adding more users to your Postmark account, you can also assign them access to specific servers so that they can’t view email activity or change settings across your entire Postmark account.
In Postmark you need to have a confirmed sender signature or verified domain for each email address you want to send from. Sender signatures are individual email addresses that are authorized for sending via a confirmation email sent to that address. Adding and verifying a domain using a DKIM record lets you send from any email address on that domain.
We use sender signatures and verified domains to ensure you own or are authorized to send from the mailboxes you add to your Postmark account. You can have as many signatures and domains as you need, there is not a limit. Sender signatures and domains are associated with your account, not a specific server. This means they can be used for sending across all of your account’s servers.
Tip: You can use any sender signature/verified domain for sending with any Postmark server, from any location. You do not need to verify the same domain multiple times for using with different AWS regions.
Each Postmark account has an account API token. Every server in an account also has its own server API token(s). Server API tokens are used for server-level actions such as sending email, getting statistics, modifying a template, etc… account API tokens are used for account-level actions such as creating a new server or adding a new domain for sending.
Like SES’ firstname.lastname@example.org test address, you can also send test emails to Postmark’s sink email address, email@example.com. Messages sent to this domain will be dropped on the receiving end but you will be able to see the delivery confirmation and message in your Activity. Also check out our blog post about best practices when testing with your Postmark account.
Entire domains can be verified for sending using DKIM records.
The maximum message size, including attachments, is 10 MB with both SES and Postmark.
Postmark messages can also have up to 50 recipients in a single message, which is the same as SES.
Postmark does not have sending quotas or maximum sending rates that you have to adhere to or request increases on.
You only need to verify a domain or individual email address for sending with Postmark once, whereas with SES you may be used to verifying the same domain multiple times for each AWS region.
There is only one SMTP endpoint with Postmark (smtp.postmarkapp.com), unlike SES, which has three different endpoints for different regions. We will automatically route you to the nearest data center when connecting to smtp.postmarkapp.com.
SES allows sending messages using a raw MIME format, which is not supported by Postmark. Emails must be sent through Postmark’s API or SMTP using the MIME components (To, From, Subject, etc…).
You must use a Server API Token for both your SMTP username and password when using SMTP with Postmark. You can generate as many Server API Tokens for each Server as you need.
Templates are not supported with Postmark’s SMTP service and can only be used with the Postmark Templates API.
In addition to adding a tag, you can also add custom metadata(link to faq) to messages sent using Postmark.
Verifying Email Addresses and Domains for Sending #
Similar to SES, domains in Postmark can be verified for sending using a DKIM record added to your domain’s DNS. You only need to use a DKIM record to verify a domain in Postmark, similar to SES. Head over to our help article on verifying a domain for sending with Postmark for more detailed steps.
Once you add DKIM for a domain in Postmark, it is applied automatically to all emails sent from that domain, without an option to disable it at the message or sending email address level. Similar to SES, we will also periodically check your DNS to make sure the TXT record for DKIM is still in place. We do not completely remove domains from your account if we do not detect it, though. If we find the DKIM record is not present, we will pause signing with DKIM and send you an email notification so you are aware and can get the record back in your DNS.
With Postmark you only need to verify a domain once, you do not need to complete the process for multiple regions like you do with SES. Sub-domains are also not automatically verified in Postmark once you verify a root domain. Each sub-domain you want to send from will also need to be added to your Postmark account and verified with DKIM records.
Postmark, like SES, also includes an additional option for sending from a single email address that you can confirm using an emailed link. You can add individual addresses as Sender Signatures to your account, which does not require that you add a DKIM record to send with that email address, though we always recommend setting up DKIM and a custom Return-Path to maximize deliverability.
You can add and manage your sending domains and email addresses from the Sender Signature page in Postmark. Each domain you add has an Authentication page that includes the unique DNS record information for setting up DKIM and a custom Return-Path.
Tip: Postmark does not allow sending from any public domain email addresses, such as Gmail, Yahoo, AOL, Outlook, Live, etc…
Each server you create in Postmark will have its own unique server API token(s). You will need to use a server API token (found in the credentials tab of a server in Postmark) for authenticating SMTP sending. If you need multiple sets of credentials, you can either create multiple Servers in Postmark (since each Server has its own unique token) or generate additional Server API Tokens for your single Server.
Tip: Port 2587 is not supported with Postmark SMTP. If you were using that port with SES, you will need to switch over to using port 25, 2525, or 587 when using Postmark SMTP. We recommend using port 2525 or 587, since port 25 is sometimes blocked or throttled by ISPs.
When authenticating with the Postmark API for sending emails, you will need to use your server API token in an X-Postmark-Server-Token header, similar to the X-Amzn-Authorization header in SES. As a reminder, you can get your server API token from a server’s Credentials tab.
How inbound email processing is implemented is very different between Postmark and SES. If you were using inbound processing with SES and will be using Postmark for processing email once you migrate, this section is an important read.
Postmark’s inbound message size limit is 35 MB compared to SES's limit of 10 MB.
Postmark does not require you to take any actions to preserve inbound messages. We will automatically keep them in your Activity and available through the API for 45 days.
Specific actions based on the recipient (Receipt Rules / Receipt Rule Sets in SES) cannot be set in Postmark. Your code for your inbound webhook URL would need to take care of any additional processing tailored for specific recipients.
It is not possible to block inbound messages by their source IP. Instead, Postmark provides inbound message blocking based on the sender's email address, sender's domain, and SpamAssassin spam score.
With Postmark, you do not have to use a verified domain for inbound domain forwarding, and Postmark does not require that you set up inbound domain forwarding using an MX record in order to use inbound processing. Each server you create in Postmark will come with a unique inbound email address (ex. firstname.lastname@example.org) that you can use to receive emails inbound at your webhook URL. However, if you want to use inbound domain forwarding, and MX record is required.
Postmark receives inbound emails, converts them to JSON, and POSTs them to your inbound webhook URL, rather than processing them using Receipt Rules that route the messages to an S3 bucket, Amazon WorkMail, or SNS notification.
You can use a wildcard in your MX record to have all sub-domains of your domain point to Postmark for inbound processing.
Postmark requires that you enable SMTP (if not enabled already) on your Postmark server to use inbound processing.
In the event your inbound webhook URL fails to send a successful response to an inbound message, a total of 10 retries will be made by Postmark, with growing intervals from 1 minute to 6 hours. If all of the retries have failed, your inbound activity page will show the message has a processing error.
Headers cannot be added to inbound messages in Postmark.
Somewhat similar to Event Publishing using Configuration Sets in SES, Postmark allows you to receive notifications as JSON POSTs to URLs you specify when specific events occur using webhooks. With Postmark, you are no longer forced to use CloudWatch, Amazon SNS, or Kinesis Firehose to receive events, since you can use any URL for receiving webhook events with Postmark. Postmark webhooks are sent in real-time as message level events occur, meaning each POST to your webhook URL is for a specific message. Postmark has unique webhooks for each event type (Open, Delivery, Bounce, Inbound message) rather than a single source that specifies the event with an event type parameter.
Postmark’s delivery webhook allows you to receive notifications when an email is delivered to a recipient. In Postmark, an email is considered successfully delivered when the destination email server returns a 250 OK response after delivery is attempted.
Postmark includes some additional information for bounce events that is not present in the SES event notification you should be aware of:
The Postmark server used to send the email
Information on whether the recipient’s email address is deactivated and can be reactivated
Whether a message dump is available. Postmark stores content for 45 days but retains bounce information indefinitely. If the message was sent less than 45 days ago, you can get a full dump of the message content if this parameter’s value is true.
Whether the recipient’s email address can be reactivated
If a message dump is available
Tip: Postmark includes an additional option when setting your bounce webhook URL to include the message content in the JSON sent to your URL. This option lets you receive the full message content when receiving bounce event information.
When you log into Postmark you are placed in the servers page, which shows each server you have created. Each server you create has tabs for Statistics, Activity, Templates, Settings, and Credentials, which are unique for each server in your account.
Servers let you separate your outbound and inbound messages, templates, and credentials based on domains, environments, customers, or any other criteria that helps organize the activity of a given application or website.
The main servers page will show you a list of your servers. You can create as many servers as you need, there is no limit. You can also pin your most frequently accessed servers so they appear at the top of the list. Unused servers will be greyed out, for easy identification of which servers you may want to delete or repurpose.
To view statistics and metrics for a server, click on the server, which will take you to its statistics tab.
The statistics tab is similar to the aggregate metrics you can view with SES, though each server has its own statistics page, rather than an overall account view. Included in the statistics area are the server's sending volume, processed (inbound) volume, link tracking metrics (if enabled), open tracking metrics (if enabled), and bounce metrics.
Coming over from SES, you might not be used to being able to quickly view sent and received messages in a friendly UI, without having to do any additional setup. With Postmark, you can quickly search and view your sent and processed messages without any extra effort or development work. Postmark will automatically store and display all successfully sent messages for 45 days and all bounces indefinitely.
To see your inbound and outbound activity in a server, click on the Activity tab. This area will show a detailed event view of that Server’s events, including sent, delivered, open events, spam complaints, bounces, etc... Use the search bar to look for emails by subject or email address.
To see details for a particular event, click on the event. Some events included are sent emails, bounces, spam complaints, clicked links, and opened emails. Events in Activity are color coded to help you tell what occurred at a glance:
Postmark gives you the ability to create and store templates including a variety of pre-built and well-test templates for common scenarios. From the Templates tab you can create, edit, and delete the server’s templates. Each server contains its own templates but you can easily copy templates from one server to another.
Alternatively, if you'd like to build your own batch of templates, we've created and open-sourced MailMason to help you automate the process of creating, testing, and managing your own templates using partials, variables, SASS, and asset management.
The Account page is where you can add emergency contacts in case we need to reach you regarding your account and have not heard back from the owner, set up billing notifications, mange your account API tokens, manage your subscription, and other administrative features.
The Users page is where you add and manage users to your account for tasks such as viewing activity for troubleshooting and tracking purposes, managing server settings, creating templates, etc... Use our different roles to effectively manage the security of your account. See our help article on setting permissions for an overview of what options there are and how to control your users’ permissions.
For more Postmark specific insight on how to get started and get the most out of Postmark, make sure to look through our “Getting Started Guide” or visit our support center where you can easily search all of our documentation from a single place. API docs. Guides. Blog posts. Help docs. Labs projects. You name it. We probably have something that can help you out.
Once you've switched to Postmark, you may want to become familiar with our status page and status API. We believe deeply in transparency, and we go a step further than just system availability and share our inbox rates and delivery speeds for the five most popular inbox providers. We also offer all of the data via an API so you can monitor us and set up automation in the event something does go wrong.
You now have a solid understanding of how to transition over the core features you need in an ESP and how to move from Amazon SES to Postmark, including how to send outbound and process inbound email, what APIs and webhooks to use for certain functions, and how to view your email activity and statistics. If you have any questions about where to find a setting or how to use a feature in Postmark, get in touch and we can help!