Easy-SMTP rate limits and recommendations

Invalid addresses are processed asynchronously, and Delivery Status Notifications (DSNs) are streamlined to improve results.

Connection Limits:

• 100 RCPT commands per message (RSET command reset the counter)
• 25 messages per connection 

For best performance it is recommended that senders maximize connections as efficiently as possible. For example, if you send the same message to 5000 recipients this can be accomplished in two connections. Each connection would ship 25 messages, each to 100 recipients. Multiple connections can also be maintained concurrently. 

DSNs (Delivery Status Notifications)

Easy-SMTP no longer blocks known invalid addresses at the SMTP layer. Long standing customers may remember the "550 Address Blocked" responses during the connection stream. All RCPT commands will be met with a 250 OK response.

In order to best serve our customers, we now process known invalid emails asynchronously. DSNs will be delivered to one of the following address listed in order of preference:

1. Return Path
2. Envelope Sender (MAIL From command)
3. From address

Only one attempt will be made to deliver DSNs for known invalid emails. Customers should ensure that the Return Path address is able to accept and process incoming bounce DSNs for best results.