I've recently started having trouble sending to mimecast servers. What happens is that my server will connect, then nothing else happens, and the connection times out. This will happen for each of the servers listed in the recipient's domain's mx record, six of them, then the message bounces. This does not happen every time, about once a day I can get email delivered to them. What I *think* is happening is that they are stealth blocking me based on the network my IP address is on (belonging to Spectrum) rather than my IP address having ever sent spam or been on a blacklist. I'm not even on APEWS anymore.
Mimecast doesn't like talking to senders, so I am having a lot of trouble getting support from them. They also ask me to email them the .eml files involved, then block the email I try to send them. I've even tried sending from another email account. Before I get my ISP involved, and ask the recipient's IT folks to get involved, I'd like to be sure I'm not missing anything. I've done all the mail testing I still have links for (unlocktheinbox being lo longer).

Has anyone experienced this before with mimecast? If so, how did you resolve it?

(This for SmarterTools) Why does the message not go into retries on an SMTP timeout like it does for SMTP errors? If it did, I imagine my outgoing emails would eventually get through, based on the frequency with which they do when I manually re-send.

Any other input would be appreciated.

Thanks,
Pat

Here's what the log looks like:
11:38:50.331 [23990219] Delivery started for {me} at 11:38:50 AM
11:38:53.346 [23990219] Added to SpamCheckQueue (1 queued; 0/30 processing)
11:38:53.346 [23990219] [SpamCheckQueue] Begin Processing.
11:38:53.346 [23990219] Blocked Sender Checks started.
11:38:53.565 [23990219] Spam Checks started.
11:38:53.565 [23990219] Spam Checks skipped: User authenticated
11:38:53.565 [23990219] Spam Checks completed.
11:38:53.565 [23990219] Removed from SpamCheckQueue (0 queued or processing)
11:38:56.348 [23990219] Added to RemoteDeliveryQueue (1 queued; 0/50 processing)
11:38:56.348 [23990219] [RemoteDeliveryQueue] Begin Processing.
11:38:56.348 [23990219] Sending remote mail from {me}
11:38:56.442 [23990219] MxRecord count: '2' for domain '{recipient domain}'
11:38:56.692 [23990219] Attempting MxRecord Host Name: 'us-smtp-inbound-1.mimecast.com', preference '10', Ip Count: '6'
11:38:56.692 [23990219] Attempting to send to MxRecord 'us-smtp-inbound-1.mimecast.com' ip: '205.139.110.221'
11:38:56.692 [23990219] Sending remote mail to: {recipient 1}, {recipient 2}
11:38:56.692 [23990219] Initiating connection to 205.139.110.221
11:38:56.692 [23990219] Connecting to 205.139.110.221:25 (Id: 1)
11:38:56.692 [23990219] Binding to local IP {my ip} (Id: 1)
11:38:56.738 [23990219] Connection to 205.139.110.221:25 from {my ip}:60949 succeeded (Id: 1)
11:41:56.751 [23990219] The smtp session has timed out.
11:41:56.751 [23990219] Attempt to ip, '205.139.110.221' success: 'False'
11:41:56.751 [23990219] Attempting to send to MxRecord 'us-smtp-inbound-1.mimecast.com' ip: '207.211.30.221'
11:41:56.751 [23990219] Sending remote mail to: {recipient 1}, {recipient 2}
11:41:56.751 [23990219] Initiating connection to 207.211.30.221
11:41:56.751 [23990219] Connecting to 207.211.30.221:25 (Id: 2)
11:41:56.751 [23990219] Binding to local IP {my ip} (Id: 2)
11:41:56.798 [23990219] Connection to 207.211.30.221:25 from {my ip}:60952 succeeded (Id: 2)

And that repeats until each IP has been tried and timed out.