Rules for ESP

This article is useful for Email Service Providers (ESPs) and their customers.

We recommend reading the general requirements for all senders in section "Mailing rules”.

Technical requirements for ESPs

1. For each customer, use its domain in the “From” field.
• Do not use free-mail addresses for email distributions.
• Do not send a customer’s email distribution from the ESP’s domain
2. Each email must be DKIM-signed by both the ESP and the client’s domain (this is extremely important in order to avoid mixing up reputations).
3. For domains with a DMARC policy, verify that the source of your emails is correct.
• Keep in mind that an existing customer may also enable/turn on a DMARC policy (including p=reject).
4.  Sign the mailings headers.
• Precedence: bulk
• List-Unsubscribe: <valid link to unsubscribe>.
5. The email headers must be clearly associated with a specific ESP (multiple DKIM, Received, other headers).
6. Follow the RFC when forming the envelope and message body.

Support for mailings, including from individual clients

1. Use statistics on Postmaster:
• Regarding your own DKIM (track your reputation).
• Regarding the client DKIM, if possible (track your client’s reputation).
• Regarding the types of client mailing (track the reputation of specific types of email using X-Mailru-Msgtype.
2. Promptly process the FBL and “List-Unsubscribe” header (immediate unsubscritpion after a click).
3. Implement/use deliverability monitoring (for clients as well as for each ESP as a whole).
• Statistics on Postmaster.
• SMTP replies with 4xx codes
• SMTP replies with 5xx codes
• Delivery to Spam folder
4. Avoid “questionable” methods used by the client: replacing addresses in the “From” field, using redirects, etc.
5. Track how organic customer base growth is and changes in the statistical parameters of email distributions.
6. Develope monitoring means that make it possible to remove inactive users from the database.

Preventative measures to reduce the number of complaints and spam

1. Verify ownership of the domain.
2. Deny or moderate bulk emails distributed from trial accounts to real databases via the service. Messages from trial accounts must also have headers with an appropriate X-Mailru-Msgtype: trial-<> mask.
3. For new clients:

• Be sure that subscription’s DOI mechanism works
• Evaluate the database’s quality using third-party and/or in-house services.
• Perform A/B testing on small segments of the database and determine the ComplaintRatio and SpamRatio.
• Identify clients sending mailings from several domains (including using the header).

The list of rules includes the most critical requirements which, if not followed, may impact email deliverability for individual clients, as well as email deliverability for the entire ESP.

If you are an ESP’s customer, find out whether your ESP follows these recommendations. The answer could determine whether your messages are delivered or not.