If your your server account details are correct and the server has no issues, the most common cause is there is some type of program on your computer interfering or blocking EM Client from access.
If you have any optional eg: Firewalls, Security Programs, Antivirus programs, Malware programs etc try disabling those and close and reopen EM Client, and click the (Refresh) button top left to check for email and see if you then get email.
If you then get email, you have to configure whatever program was blocking the mailer to then “Allow” EM Client access.
However if you have no optional firewall / security programs, anti virus , malware programs etc or disabling any optional programs as in the examples above didn’t make any differance, then could be you either you have some sort of corrupted EM Client account and needs removing and re-adding again, or the EM Client program you are using has some issue and needs uninstalling and reinstalling.
So to uninstall EM Client to see if program related, click “Menu / Backup” within EM Client, and then uninstall EM Client and when asked do you want to delete the database, “Choose No” not to delete and complete the uninstall.
Then download the latest version of EM Client if you don’t have it already from the Version History page https://www.emclient.com/release-history? and reinstall. EM Client will pickup your existing database and should open and hopefully will start to receive email.
If you still get the Red Triangle, then next thing would be to “Remove your account” from EM Client and “Re-Add your account”. If you are going to do that, i would suggest to “Do another backup first”.
Lastly if neither removing and reinstalling the program or removing and re-adding the account makes no difference, click the “Red Triangle” and go to the “Log” tab and copy the contents to this thread so we can look for any obvious errors.
Also what version of EM Client are you using and what Account & Server settings are you using. Also do you have Windows or Macintosh.