To clarify, sendmail is not a part of Perl , nor is it distributed with perl. It is a separate application. Your script just happened to be accessing the separate application. Any obsolescence in sendmail would come from itself, not from Perl. That said, a quick web search for "security concerns with sendmail" shows that many people consider sendmail insecure.

Rather than "accusing" your host, I would phrase it something like,

/usr/lib/sendmail used to exist on the server, but now it seems to not exist (in that, I cannot execute it at that path, and I cannot find it elsewhere). Was its remove a deliberate action, or an oversight during an upgrade? If it's deliberate, what alternatives do you support?

But before sending that message, I'd suggest looking for sendmail, and see whether it's really missing, or whether they just removed your permissions to execute it, or whether they moved it.

And really, the best solution, rather than pestering your host, would be to follow corion's advice

You can find out where sendmail is, information about it including whether you have permission to run it, and similar information about /usr/lib/sendmail, with commands like these:

$ which sendmail
/usr/sbin/sendmail
$ ls -l /usr/sbin/sendmail
-rwxr-xr-x 1 root wheel 243824 Jan 13 18:14 /usr/sbin/sendmail
$ ls -l /usr/lib/sendmail
ls: cannot access '/usr/lib/sendmail': No such file or directory
[download]

You can get similar information by writing a script that uses the file test operators.

It seems that sendmail module has been removed by my host. ... I don't want to accuse my host of removing sendmail unless there is a good reason.

If the module is not there any more, it would seem to be reason enough to say it's been removed. ;-)