Hopefully, someone can answer this for me.
We migrated from our old mail server to the new Ensim/ME Pro server this weekend. Yesterday AM when our reporting dept starting sending reports to one of our clients (attachments around 5meg to muntiple recipients) and they received multiple "Message Delivery Failure" notices like this:
The following recipient(s) could not be reached:
[SMTP:email@example.com]: 421 4.3.0 collect: Cannot write q/dfh9KFLAqJ009312 (sm_io_flush||sm_io_error, uid=0, gid=198): Input/output error
According to the SMTP logs, it's only happening when opur mail server connects to 1 of 3 client incoming email servers. And it is not happening on every email that is sent to that server. The 421 error appears right after the DATA 354 Enter mail, end with "."....... line on a DATE line where we usually see a 250 ...message accepted for delivery. The server logs yield no application, system or webppliance errors.
Is the 421 error indicating a problem with OUR server sending/saving the message or a message from THEIR server saying that the SMTP service is not available?