gmail is fancy and offers lots of space
I do however have several arguments against using gmail that make me not using it myself for anything that is critical.
gmail blocks zip files
The main and major complaint can be phrased like this:
(reason: 552 5.7.0 Illegal Attachment p9si2809195fkb)
That’s the exact message gmail includes in the reject mail when I try to mail my own account with a zip file attached. The zip file itself is perfectly harmless (and contains source code).
I actually get completely legitimate zip files from people every now and then, perhaps even once per week or so and having it reject these mails without even properly explaining why to the user is quite a show-stopper!
gmail spam filter is inferior
The other issue I have with gmail is its annoying spam filter. This too is often claimed to be one of the better things with gmail, and given that they have millions of users and can do pretty detailed statistics on received mails they do have the opportunity to make a decent filter.
But, given that the spam filter is one huge you-have-no-choice-but-our-way there’s no way for me to alter configs, tweak it for my specific spams or make it better deal with the false positives that it picks. And I’ve had it catch far more false positives than my regular spamassassin filter on my main mail account and then I get probably a thousand times more mail and spam on that account.