Quoting Russell Coker (russell@coker.com.au):
It's been a long time since there were multiple choices for sshd.
{chuckle} Through rotten luck, you made that claim to the person who maintains the master list for the Internet of SSH software for all platforms.[1] I recommend Dropbear to your attention particularly. http://linuxmafia.com/ssh/unix.html
MTAs vary in support for Milters and the various obscure command line options for the sendmail program.
Hey, man, I remember milters! I remember sendmail, even. Man, that'd be nostalgic if it hadn't been so awful. If I were forced to pretend it's still 1985, I could even run it the way I did for a decade or so. You assertion is correct but irrelevant to the point. Being a senior system administrator, I can reimplement what I do in any of exim4, postfix, Courier-MTA, or several proprietary MTAs for *ix in any of the others in about an hour or two.
If you need more than that then it becomes very difficult.
No, I do not find that to be the case. However, effective antispam is difficult (and necessary) on any MTA. [1] Honestly, that catalogue has become increasingly pointless, but I was motivated to create its original version by hearing the stunning claim in the early 2000s on a University of California at Santa Cruz Linux mailing list that it was absolutely necessary to continue using unencrypted telnet for remote logins around the university network because no ssh implementation existed for OpenVMS. Rather than respond as expected, that it's ridiculous to compromise everyone's security for an obsolete and insignificant operating system, I researched the factual claim and found that there were actually _multiple_ implementations for OpenVMS: http://linuxmafia.com/ssh/openvms.html