Typically outgoing mail server errors indicate an issue with sending email; this is often the result of a misconfiguration in your email client or your ISP blocking important ports.
We recommend using your ISP’s outgoing mail server in your email client, as this works around any port blocking they may have in place.
Your outgoing mail port will be 25 when using your ISP's outgoing mail server. If you experience issues connecting to your ISP’s outgoing mail server, your first port of call should be their support line.
If you’re using your web hosting server for outgoing mail (i.e. mail.domain.com), then it’s possible your ISP is blocking the outgoing mail port. Within your email client we would recommend, where using mail.domain.com as your outgoing mailserver, than you change the outgoing mailserver port from 25 to 587. This should alleviate your issues.
Additionally, when using the hosting server for you outgoing mail you will need to enable “Outgoing server requires authentication”.
