SMTP host or IP. If you are using the PHP mail function, you should set this to "localhost" or whatever is
required by your server. If you are using SMTP, check that your server actually supports SMTP. Other servers block SMTP from certain services, such as Office. If you have issues, enable the mail debug log. See below.
IMPORTANT: If you are using Gmail, DO NOT use your Gmail password. You MUST create an app specific password in your Google account and use that. Also,
ONLY use SSL if you have SSL installed. If you don't, you should use TLS. For the Gmail port ONLY use 465 or 587.