Custom SMTP server

[TVC]

Hi, i'm setting up a custom smtp server but when i fill in all the information and click test, an error appears as shown below. please help me, thanks.
I use 3cx v18 and ENT edition.

 

[Marconi]

What sort of SMTP server are you using? How is it configured? Does it force the use of SSL/TLS? Is you SMTP server using a self-signed certificate?

Please provide more information so that we can help you resolve your issue. Thank you.