That’s not directly to Discourse via the HTTP POST API which is what this topic was about…
GMail is acting as a middle man and this delays the processing of emails into Discourse by 1 to 2 times the POP3 polling time.
There are a few other POP3/Gmail issues which use of the direct mechanism resolves.
One thing you don’t get is Gmail’s superb SPAM processing. However there is already a decent level of protection both in the mail handler and Discourse especially if Akismet is installed.