550 [internal] [oob] The recipient is invalid.

[Matt_Moore1]

Has anyone ever seen this Email Invalid Cause? Looking for support on this. Thank you!

[Hobie_Thompson1]

This could mean a variety of things, though most likely that the email address, for one reason or another, is invalid. The thread here gives some good details:

What does "550 internal oob The recipient is invalid" mean ? ...... Hard Bounce / Soft Bounce ?

Specifically, look at Mike Reynolds​ reply at the bottom of the thread. It gives some good clarity into the "[oob]" part of that error code - basically, the email server said it would accept the email, but then bounced it. (so don't count on the "550 [internal] [oob] The recipient is invalid." error to mean "the email isn't valid" - this is possible, but not the only option.)

[Gerard_Donnell4]

Hi Matt Moore​,

The 550 message is an email bounce.  The "oob" stands for "out of bounds".  There is a previous thread about this with links and more in-depth explanations. What does "550 internal oob The recipient is invalid" mean ? ...... Hard Bounce / Soft Bounce ?

Thanks,

Gerard