User mailbox is unavailable.
Causes
- A process on the remote server is tidying up the mailbox
- The remote mailbox could be corrupted
- Remote mailbox may be stored on another server which is now offline
- The network connection went down while sending
- The remote mail cut off would prefer not to acknowledge mail from your server for reasons unknown. For example,
- IP Addressing, blacklisted
Fixes
Step 1: Email Account Exist
Make sure the email account does exist.
Step 2: Contact Client
On the off chance that you have elective contact technique for the client, get in touch with them making mindful of the issue.
Step 3: Check IP Addressing For Blacklisting
Check your mail server IP address for blacklisting.
Step 4: Check For Malicious Content
Browse your email message for malicious or “spammy” content.
Step 5: Send Without Attachment
In the event that you have an attachment, have a go at sending without one.