We have Kayako helpdesk running on our WHM Linux server.
When e-mails come in from customers, notifications are sent out by Kayako to a number of staff whose mailboxes are hosted on Rackspace mail servers.
I noticed a large queue in the Exim queued message viewer of WHM - when looking in Exim logs I can see many lines
2012-10-13 20:06:56 1TN72s-0007Cw-1l SMTP error from remote mail server after initial connection: host mx2.emailsrvr.com [184.108.40.206]: 421 Too many concurrent connections from this client.
One client email results in about 5 emails to rackspace servers, perhaps 60 emails per 1 hour on average - not a huge amount but enough to cause messages to be rejected when sent in short bursts.
In this case ideally if we can limit the connections sent to the rackspace server we can comply with their limit. For our requirements if we send 1 email every10 seconds or so, this would be OK.
Messages to all other servers should go through a normal rates, only mx1.emailsrvr.com and mx2.emailsrvr.com should have this connection limit policy applied.
Is this possible?