The mail settings for Celoxis are no different than the settings made on a mail account. So, if you are able to send/receive mails from this account, then you should receive or send mails to Celoxis. To test this:

IMPORTANT This testing needs to be performed on the server where Celoxis is installed i.e the email client needs to be setup on Celoxis server.

Your mail administrator must have created an email account on the mail server; for e.g celoxis@acme.com
On the server where you have installed Celoxis, setup your mail client (Outlook, Thunderbird, etc) with the following:
1. For sending mails from this account (Outgoing Mails in Celoxis), setup the email address in the email client as celoxis@acme.com
2. For this account to receive mails (Incoming mails in Celoxis), setup the email address in the email client as celoxis@acme.com
Now, send an email to this account from any other email account (from the same server). Check if the mail is received by celoxis@acme.com
This confirms that the Incoming mail is working.
Again, from the same server, send an mail from celoxis@acme.com to any other email address. If the mail is received by that email account, it means that the Outgoing settings is working.

If however, you are unable to send/receive emails to/from Celoxis, then check the following:

On your mail server, the email account is enabled (with their respective protocols).
You have entered the details carefully the same way you have entered when testing your mail account i.e. the port number, the protocol, etc.
The Celoxis server is able to reach the mail server i.e there is no connection, firewall issue blocking the connection.

If you are not able to investigate, then open a ticket with the following:

The debug bundle; 4-5 minutes after you have performed an operation.
Mention the operation performed (task assigned, create task via email) with the name of task or the email subject which was sent to Celoxis.

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