Deferred: Input/output error [MS Exchange]

Hi comp.mail.sendmail,

I would like to share my experience with resolving following error in its certain incarnation:
----- Transcript of session follows -----
451 4.4.1 reply: read error from
<someaddress@xxxxxxxxxx>... Deferred: Input/output error

After I have released recompiled version of Sendmail into production few weeks ago, intermittent issue with email delivery to some recipients from our SMTP servers started occurring.

We have traced the issue to MS Exchange, specific versions we had troubles with are : 6.0.3790.4675 and 6.0.3790.1830

New compilation of sendmail binary was done with openssl 1.0.1, when I have reverted back to 0.9.8u - communication error with MS Exchange vanished.

I clearly understand that there is no Sendmail guilt in that, it works with openssl-1.0.1 perfectly. Just wanted to give a heads up to anyone who encounters with the same issue, since I have spent few days thinking of what could it be before actually went to solution.