Hello everyone good night.
Now appreciate any help from you, thank you very much for real.
I'm using zimbra less than two months and I'm running into some details and drawbacks and do not know how to solve them. Today I use one in serveraxis.com vps, vps that has 4GB of memory and installed "Ubuntu Linux 4.12 x86_64", I use the open source version 8.0.3.
Well with this information I believe you can already get an idea of what I'm using.
The problem is the following ... first problem, sometimes when sending emails (webmail) these tend to take a long time to be delivered at the click send almost instanteamente already shows that it was sent, but the user takes to receive it.
Another problem is the following, the daily report that I receive at the very end have the following information

"Warnings
--------
** smtpd (total: 37)
******** 18 server.domain.net hostname does not resolve to address xxx.xxx.xxx.xxx "

This is already causing some problems, could you please help me solve these two issues?

Thank you!