Inbound SMTP Restrictions

Inbound SMTP Restrictions

In order to provide the highest level of service our inbound injection network has the restrictions listed below when injecting inbound messages for relay.

-Maximum of 20 simultaneous connections per IP may be established to

-Maximum message size, including any embedded images and attachments, is 40MB

-Maximum 500 total recipients per message

For optimal performance, please limit the number of messages per connection to 50.

More Information

See our other articles for more information on related topics.

IP Addresses, Ports, and more inbound SMTP connection information: SMTP Connections

To better troubleshoot and diagnose SMTP connectivity issues see our blog on Diagnosing SMTP Service Connection Issues 

Related Errors

If your message is larger than 40MB you will receive the following error:
552 5.3.4 - Message too big for system

If you attempt to send to more than 500 addresses in one message you will receive the following error:
452 5.5.3 - Too many recipients

If you attempt more than 10 connections you will receive the following error:
421 4.4.5 - Too many connections from your host