[jholman]

It depends on whether you think "ungrammatical" means "not approved of by prescriptivists", or you mean "not used and/or not understood by fluent speakers".

Given that you know the word "pro-drop", I assume you know this, and I'm not sure if I should bother continuing in this vein. Maybe you're asking for a descriptive grammaticality judgement from fluent English speakers?

I agree that from a prescriptivist perspective, this is improper formal writing.

From a descriptivist perspective, I try to avoid biz guys, but I suspect the GP post nailed it, with respect to common usage in the appropriate sociolect (the same sociolect that has "proof points", "value-add", "circling back", etc). Although maybe not for the last sentence of an email that already had that much circumlocution.

[Evbn]

Ungrammaticality changes over time. For a new grad emailing her boss, douchy pro-dropping in English is ungrammatical. Eventually, it sinks in as an acquired taste, and becomes grammatical.

Hey, is it ungrammatical to call a woman Douchy?