Common 550 errors:

One of the common error occurred in web hosting is 500 error. It has many reasons to causes 500 error. If emails are bouncing across from the different receptors when sent from sender to recipient, then there is an error message generated due to mail relay on the server. It has several types of 500 error messages. Some of them are listed below in this article.

550 SMTP error:

This error has occurred when you are using the mail client. While configuring the mail client, check the box “My SMTP requires Authentication” to avoid this error. This is the main cause of this error.
Another reason is maybe you have not logged in your IMAP server for the last 30 minutes. This error can also be generated in another form as ‘550 senders verify failed ‘ error.

550 No such users here:

This message generated while your DNS configuration in the server is set to localhost manager or automatically managed settings. For example, if you are having a hosting account in one hosting provider, but you are maintaining your emails in Gmail or Yahoo,
the DNS settings should be checked in remote mail exchanger. If your hosting provider checked it to local mail exchanger or Automatically exchange emails, then you will face this error while sending emails.

550 External MTA’s must be authenticated:

While configuring outlook, you should check the box “My SMTP requires Authentication” to avoid this error message.

550 Dictionary Attack:

Spammers use this method often. They have tried to send the various emails and passwords to a particular domain hoping that one will get succeeded. When they are attempting this method, the server will detect it, when four consecutive invalid email address or passwords. Then server generated this error message and blocked the Dictionary attack. You should be stopped during the sending process as well as your mail lists. To overcome this error, try to send the emails after one hour. If you are using any mail clients, try to send emails by using webmail.

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