Queue slow to delivered

[brenoacp]

Hello everyone!
We have a server with multiple domains.
Users have complained that emails are slow to arrive in your mailbox.
By testing an external account and observing in the logs the email is delivered quickly on the server and then queued. Only after 4 min on average that the email is delivered in the mailbox.
Looking at the active queue we always have on average 6 emails. Is there any way to improve this?
It appears that the server processes one-to-one mail to deliver the mailboxes.

Best regards,
Breno Padovan