Attached to gmail, a third-party account slows down sending and receiving messages. What's the matter?

Question

gmail

There is a domain attached to a regular shared hosting, there is a mail server on this hosting.
Several mail accounts are created, which are then attached to the corresponding gmail accounts for sending and receiving messages.
For example:
1) [email protected] to [email protected]
2) [email protected] to [email protected]
Etc. etc.
The problem is as follows:
1) The delay in sending and receiving messages, after sending via gmail, the data goes to the server and is processed there from 1 to 15 minutes at least
2) Messages from one addressee to another do not periodically arrive within this group of addresses on this hosting
3 ) There was 1 case with the substitution of the addressee.
Example:there is a chain of messages within a group of recipients, one of them answers in correspondence. As a result, he and the other participants see such a picture, the letter in the sender has a mail address not from the desired address (let's say [email protected]), but from one of the participants in the correspondence, and the funny thing is that this is the gmail mail address of another participant (that is, the person is listed in the [email protected] correspondence, but he was attached in the letter as [email protected]) I
used to notice that the mail attached in this way in the gmail account slowed down a little, but did not buggy in this way.
What can you advise dear readers)?

Answer 1

gmail sends through a third-party smtp, so the logs and see
the routes inside gmail are made taking into account the avoidance of loopback, which means sometimes something may not be sent