Why is mail from one server to different gmail boxes delivered with a difference of a couple of hours?

Question

Email

From our server, which operates on Moscow time, we send letters. One for myself to check, the second for clients on their gmail. It comes to us almost instantly, but to them (in Kemerovo) it comes in 2 hours.
Doesn't go to spam, nothing bad happens, but after 2 hours. In which direction to dig?
ps Check forcibly new letters.

Answer 1

Ask for the headers of the letter, by Received it will be seen on which server the letter rested for 2 hours (or it will be seen that everything is fine and somewhere there is confusion with time zones). Further on the logs on this server, see why it could not go further.