You should use port 25 on your SMTP server and you should not have problems, if you are using smtp server with FQDN instead of entering the ip address of the server check your DNS settings on the CUE. There are different situations.
More information is needed to provide the right solution if not any of the above.
if you use an internal Exchange server you are on the right side if you use the IP Adresse over port 25 of the Exchange Server and an login user and passord which is allowed to send Emails. Don´t forget, you can only send to email addresse wich are in the domain!
Otherwise if you have no Exchange Server in this subnet, you have to use any external SMTP Server like Gmail, gmx,... please use also the IP Adresse instead of the FQDN. With an external SMPT Server you can send your messeges to any email addresse.
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