Microsoft Outlook can not communicate with Postfix
This week I received a incident that someone was unable to send e-mails (it suddenly stopped working) and shortly after that, another incidicent with the same issue was received. In both cases Microsoft Outlook was used as the e-mail client and Postfix was running on the (e-mail)server.
TL;DR: this out-of-band patch fixes the issue.
The postfix logs did not show any concrete errors:
postfix/submission/smtpd[8479]: SSL_accept error from some.rdns.entry[1.2.3.444]: lost connection postfix/submission/smtpd[8479]: lost connection after STARTTLS from some.