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And also being a good system administrator, I had written a sendmail.cf [...]Say what? Nobody writes a sendmail.cf from scratch, unless they are crazy.
> ... that used the nice long self-documenting option and variable names available in Sendmail 8 rather than the cryptic punctuation-mark codes that had been used in Sendmail 5
Good system administrators stick to conservative, portable subsets of configuration and scripting languages, rather than bleeding edge stuff.
When they deviate, they have a clear plan. They document their choice to use something new and shiny, and they keep it separated from the default system configuration.
Since SunOS came with Sendmail 5, the upgraded Sendmail 8 should have been installed in some custom location with its own path so that it coexists with the stock Sendmail, and is not perturbed if the OS happens to upgrade that.
A good syadmin would stick that in some /usr/local/bin type local directory, and not overwrite /usr/bin/sendmail.
The consultant was not wrong to update the OS. People have reasons to do that. The consultant should have consulted with the sysadmin, of course. But even in that event, it might not have immediately occurred to the sysadmin what the implication would be to the sendmail setup.