We use SmarterMail Professional Edition, version: 16.3.6989. In the past, SmarterTools support helped us solve a problem where we weren't able to send our newsletter to ~37k e-mails, bu correctly diagnosing we had throttling enabled. Since we disabled it, the newsletter started working its way through all the e-mail list.
However, at a certain point throughout the process above, we start receiving the error below when trying to send new emails, and the error persists for *hours* after the newsletter is "entirely sent" (actually, most of the list doesn't get sent because of the error, of course). How could we prevent that from happenning? Is this a problem with our SmarterMail setup, as it was with the throttling issue, or is it on our environment? Thanks for any help!
Could not deliver message to the following recipient(s):
Failed Recipient: firstname.lastname@example.org
Reason: Remote host said: 421 SMTP Connection limits exceeded