SMTP Broken Pipe issues on UTM 9.705-3 when sending Emails with attachments

Question

I've been struggling with this now for several weeks. I'm having issues sending emails with attachments through our SMTP proxy on our UTM. 
 Over time the emails will send, but it can take anywhere from 30 mins to 72 hours to send emails with attachments and it seems size has something to do with it. I've done some much testing I'm out of ideas. 
 An email without attachment sends right aways, but attach something to it, it gets held up in the spool. 
 I've check made sure attachment size is within allowed size. I've been on the phone with support and the only idea they had was rDNS was not set up correctly, but it is, and I verified it through MXTOOLBOX and other sources. I've ran CHECKTLS and everything is ok. I'm not blacklisted. I get no errors sending to GMAIL...but emails with attachments can still take at least an hour to send. I've turned off all AV Scanning as well. 
 Below are some of the logs of errors I'm receiving. What is weird is that sooner or later they end up sending. I've verified and redone SSL Certs on my exchange server and the UTM....same issue. I hope someone has some ideas. Thanks. Oh yea, my ticket number is: #03356288 
 
 I've removed identifying email address info from logs.. 
 2020-12-08 15:02:39 hotmail.com R=dnslookup T=remote_smtp defer (32): Broken pipe: hotmail-com.olc.protection.outlook.com [104.47.56.161]
2020-12-08 15:32:03 hotmail-com.olc.protection.outlook.com [104.47.58.33]: Broken pipe
2020-12-08 15:42:09 hotmail-com.olc.protection.outlook.com [104.47.55.33]: Broken pipe
2020-12-08 15:42:09 @hotmail.com R=dnslookup T=remote_smtp defer (32): Broken pipe: hotmail-com.olc.protection.outlook.com [104.47.55.33] 
 2020-12-08 12:59:35 Remote host woodlandsbhn-org.mail.protection.outlook.com [104.47.58.138] closed connection in response to sending data block
2020-12-08 13:20:55 Remote host woodlandsbhn-org.mail.protection.outlook.com [104.47.56.138] closed connection in response to sending data block
2020-12-08 13:20:55 address@woodlandsbhn.org R=dnslookup T=remote_smtp defer (-18): Remote host woodlandsbhn-org.mail.protection.outlook.com [] closed connection in response to sending data block FROM SMTP LOG: 
 2020:12:08-16:08:12 cmhfw01 exim-out[11148]: 2020-12-08 16:08:12 1kmKvG-0001Vv-Jy SSL_write: (from [InternalIPADDRESS]:999) syscall: Broken pipe 
 2020:12:08-16:08:12 cmhfw01 exim-out[11148]: 2020-12-08 16:08:12 1kmKvG-0001Vv-Jy SSL_write error 5 
 2020:12:08-16:08:12 cmhfw01 exim-out[11148]: 2020-12-08 16:08:12 1kmKvG-0001Vv-Jy woodlandsbhn-org.mail.protection.outlook.com [104.47.56.138]: Broken pipe 
 2020:12:08-16:08:12 cmhfw01 exim-out[23778]: 2020-12-08 16:08:12 1kmKvG-0001Vv-Jy == address@woodlandsbhn.org R=dnslookup T=remote_smtp defer (32): Broken pipe: woodlandsbhn-org.mail.protection.outlook.com [104.47.56.138] 
 PLEASE HELP!