Getting ” 550 publickey_unavailable ” error while sending mail

Error: 

550 publickey_unavailable

Solution: 

The server checks SPF and DKIM keys for verifying whether a email received is spam or genuine. This is done at the spam assassin level. This means, when you receive an email, the server checks whether the SPF and DKIM of the sender is correct. In your case , the sender DKIM is not valid and hence the server is rejecting it. Please ask the remote mail server or the mail sender to fix this issue. This is not an issue from sending server side.