Why does it take so long for users to receive an e-mail?

Question

PHP

I welcome everyone!
I'll go straight to the heart of the matter. On my site, users can leave an email to receive the results of some operation. The problem is that letters can arrive late, for example, an hour! I send mail using php with the mail command. I didn’t set anything up in php.ini (because I don’t know how yet, and decided to learn right from practice). For sending mail, my personal mail with the prefix [email protected] is used
PS Please, no negative! Peace to all, and thanks in advance!

Answer 1

It is necessary to add signatures (DKIM and SPF) to the DNS records, without them the letters get into the list of untrusted ones. Therefore, such a delay often turns out to be more than an hour, even a day or two.

Answer 2

Switch from php(mail) to SMTP (authorized on the mail server).
Also, it will be useful to configure DKIM and SPF in DNS for your domain.

Answer 3

milter-greylist can delay letters from recipients. And if the sending comes from some freak like mail.ru who thinks a lot about himself, who thinks that he can ignore postal standards - there are several hours of delay - how do you do it.