Hi, with LDAP connection your users will be able to connect to their Zimbra mail account using AD password.
Here is Zimbra documentation on this topic: https://wiki.zimbra.com/wiki/Configure_ ... _Directory

Hi. does that customer use an old or unpatched Zimbra version? Maybe that server got compromised. Take a look here: viewtopic.php?f=15&t=65932

Maybe this guide can be helpful? https://wiki.zimbra.com/wiki/Configure_ ... _Directory

Hi, take a look at https://wiki.zimbra.com/wiki/External_L ... ExternalDn

Just for a bit of a laugh, I thought I'd check out the "Security Center", which bills itself as "Join this group to get the latest news, updates and alerts about security issues affecting your Zimbra product." Last update "April 15, 2019 - Phil Pearl, Security Architect&quo...

Take a look at /opt/zimbra/logs/mailbox.log and search for 500 errors.
However a few years ago I had a similar problem, it was caused by wrong ownership of the logos files. I solved running as root /opt/zimbra/libexec/zmfixperms .

Yes, you can remove Zextras trial after importing the backup. The migration process is free.

Hi, since you have Zimbra Open Source edition, follow this wiki: https://wiki.zextras.com/wiki/ZeXtras_M ... Tool_Guide

Since the parameters normally involved in these problems (zimbraFileUploadMaxSize, zimbraImapMaxRequestSize,zimbraMailContentMaxSize, zimbraMtaMaxMessageSize) are configurable either at globalConfig or server level, did you check that the parameters did correctly propagate to the new server, too?

Hi, follow this wiki article: https://wiki.zimbra.com/wiki/Steps_To_R ... ZCS_Server