Deliverability- Message error

[CIGM]

Hi there,

I have noticed that the error below is happening in most of the emails we are sending to Microsoft accounts:

Email FALIED to send. Reason USER UNKNOWN. Text: 550.5.5.0. Requested action not taken: mailbox unavailable.

Do you know what are the reasons why a mailbox would be unavailable? Is there any way to fix this?

Cheers, C

[david--garcia · Accepted solution]

Whomever you are trying to send an email delivery to, that email does not exist under that particular domain, hence;

[REQUEST]         Adobe ----  send email to someone@someone.com

[RESPONSE]      Server at someone@someone USER IS UNKNOWN

Adobe then places this recipient under quarantine.

More info --> Adobe Campaign Help | Managing quarantines

[JohnnyHawkridge]

I also have gotten this message, but only with one email address. The domain is att.net, yet I get the 550 error saying that the outlook.com mailbox is not available. The message did go through to the att.net address, but I still get this error message:

xxxxx.xxxxx@outlook.com

550: 5.5.0 Requested action not taken: mailbox unavailable (S2017062302). [AM0EUR02FT019.eop-EUR02.prod.protection.outlook.com 2023-07-28T18:40:19.371Z 08DB8F962833A069]