550 Please turn on SMTP Authentication

[Glen M.]

Yesterday, out of the blue, messages to our domain began bouncing back to senders with the message

550 Please turn on SMTP Authentication in your mail client. [removed] is not permitted to relay through this server without authentication.

This was only affecting senders that use G-mail so I added an etry to the SPF record - but no luck: +include:_spf.google.com

Suggestions?

 

[LoadFactor]

Yesterday, out of the blue, messages to our domain began bouncing back to senders with the message

550 Please turn on SMTP Authentication in your mail client. [removed] is not permitted to relay through this server without authentication.

This was only affecting senders that use G-mail so I added an etry to the SPF record - but no luck: +include:_spf.google.com

Suggestions?

Same here. This fixed the issue: Please turn on SMTP Authentication

Next: figure out what the heck went wrong.

 

[KrisG]

I would strongly suggest leaving SMTP authentication on even after you figure out what went "wrong", IMHO.

 

[cPanelLauren]

Yesterday, out of the blue, messages to our domain began bouncing back to senders with the message

550 Please turn on SMTP Authentication in your mail client. [removed] is not permitted to relay through this server without authentication.

This was only affecting senders that use G-mail so I added an etry to the SPF record - but no luck: +include:_spf.google.com

Suggestions?

To clarify this is only senders that are sending your domain mail from gmail? Do you mean senders who use gmail to send/receive their messages?