From a non-mail program, it does not work

Hello, I have a problem with a mail server. From the local network of my client all the emails work with mail programs (outlook and similar) From a non-mail program, it does not work but I do not see errors in the server log. It has the same configuration as a normal mail program. What can be what is happening? Connection if you have with the server since it arrives by pinging or telnet from that computer. Best regards,