Why do emails take a long time to arrive through SMTP?

Question

PHP

The VPS is running Exim. Through SwiftMailer I send notifications to users by email. One letter goes, on average, about 10 seconds. If you do a mailing list for several users, then you get a big freeze. I send a letter from a box on the server (I don’t use someone else’s smpt from Gmail or Yandex). Is there any way to speed up the process of sending emails? Maybe Exim somehow needs to be configured for this? Or maybe somehow you can make Exim work in the background so that the page does not hang while sending?

Answer 1

Most of all, it looks like greylisting, you need to disable it for your outgoing domain (usually it has auto-learning, if it has already received letters from this address, then it shouldn’t, but you never know who set it up before you).