On a Unix server I am using the command mpack to send PDF attachments. It works, is concise and simple to use taking away all the complexity of having to compose mail header details.

The trouble is that the operational account (ops) in sending mail produces a "From:" field with an enigmatic user called "ops". I would like to change the From: field to another account name. There doesn't appear to be an mpack flag that does this. I tried adding From: to the description file, then the email address appears in the body of the mail as might be expected. Is there a way to convince mpack to change the From: field to something else.

Does anyone know how this might be done?

Honestly, never heard of mpack before. If I were to send an email with attachments from a script, I'd probably do it with Perl.

Perl may work. All the code I have inherited is bash script and mail is done using ssmpt. This means handling a heady set of mail headers. ( hey a pun!)
Anyway My brief is to not stray into the use of other programming languages. Beside Perl would be another diversion for me. Options I have tried but found lacking are mail mailx, mutt and others. The command mpack is a single line of code that does the header creation job seamlessly except for being able to override the From field. I may have to live with that.

Does this help https://www.raspberrypi.org/forums/v...c.php?t=170717 ?
Basically, edit the ssmtp.conf file file to allow override ( FromLineOverride=yes ) & edit other fields as noted ..

yes, you can use perl. You do not need to implement anything, just use that perl script (and overwrite the from field).
Or you can do something similar in python or several other languages.
Or you can follow the link posted by chrism01 and modify your ssmtp.conf.

Additionally you may try to use mpack to convert a file and use mailx or another mailer to send it.