I have a contact with an email address that Marketo claims is invalid, yet when I reached out to the user, they claim that this address is in fact valid and operational.
This is the error message I receive for 'Email Invalid':
554 delivery error: dd This user doesn't have a rocketmail.com account (REDACTED@rocketmail.com)  - mta4372.mail.bf1.yahoo.com
Can anyone assist me in solving this?
Nothing obligates a server to give an accurate SMTP error code. So, if the mailbox otherwise is operational, they've blocked emails from Marketo even if the message doesn't literally say "no likey Marketo".
Thanks for your response. Do you think it has anything to do with the Rocketmail domain? This is not very commonly used amongst our database.
You could create a sample Rocketmail account and see if it's global. It could just as easily be local to this mailbox, though.