SMTP email slow

[autumnwalker]

I'm having a real issue with the board being slow to post messages when using SMTP on the local server. There are no issues with sending email regularly, but IPB seems to grind.

I've narrowed it down to the SMTP issue as using SendGrid API results in immediate posting. 

Is there a difference in the way IPB processes an SMTP transaction vs. something like SendGrid or Mandrill API? (I had this issue before and used Mandrill to resolve until they switched their support model).

[bfarber]

Well, with SMTP we initiate a socket connection to the SMTP server directly and post the appropriate commands. With Sendgrid (et all) we call an HTTP REST API.

The slowness could be with your socket connections (perhaps a firewall on your server scans these communications but not web connections) or it could be the SMTP server. The easiest way to confirm would be to try a different SMTP server just to confirm if it is slow as well.