I'm trying to work through an issue where a user sends a batch of emails via an external application that uses their internal Exchange server to send and receive. A user authenticates in the application via port 587 and NTLM. In a batch of 20 or more emails going to external users, less than 10 actually get delivered. I'm thinking it's a message rate limit on a receive connector prior to the emails then being sent via the send connector to their destinations.
My question is related to connections....
If an email batch consists of 6 different external organizations (domains) that are being sent to, is each domain then a connection?
Maximum messages per connection is the specific setting that I'm referring to. I'm just trying to understand what all might be in play here in the process and trying to rule out various aspects such as the send connector.