The following is a list of potential error messages that can be received while using email. Along side each error is a solution for each. 

Problem: Email I send comes back “delivery failed”

Explanation: Delivery failure, also known as a bounced email, can happen for several reasons. The wording of the error message you get will vary depending on your recipient’s email service provider. Common error messages include:

Temporary errors (No adequate servers, Connection timed out, Resources temporarily unavailable, Out of memory)

Solution: These sorts of temporary errors should resolve themselves over time.

Try this fix: Check the error message. If it says that the recipient’s email service provider will keep trying to deliver your message, then there’s no any action required on your part. Otherwise, wait a while and resend the message.

Problem: Mailbox not found, Invalid mailbox, or User unknown

Explanation: The email address you're sending to doesn't exist.

Try this fix: Check your recipient's email address for typos. Make sure it’s their current email address.

Problem: Mailbox unavailable

Explanation: Most of the time, this is the same as "Mailbox not found," but sometimes there's a problem with the recipient’s account.

Try this fix: Wait a while and try again. If it still bounces, see the previous section, Mailbox not found.

Problem: Mailbox full or Quota exceeded

Explanation: The recipient has too many messages in their inbox and can't accept any more.

Try this fix: Contact your recipient about their full inbox.

Problem: Host unknown, Domain lookup failed

Explanation: The domain for the recipient’s email address doesn't exist. If their email address is someone@example.com, “example.com” is the domain.

Try this fix: Check your recipient's email address for typos. Make sure it’s their current email address. Finally, make sure their email service provider didn’t change their domain name, like when “@attbi.com” became “@comcast.net.”

Problem: Message too large

Explanation: Most email service providers have a limit on the size of any single message that their customers can send or receive. Your message exceeds your recipient's service limit.

Try this fix: Instead of sending large attachments in the mail, upload them to OneDrive and send the recipient a link. It’s easy to upload files to OneDrive , and then send a link in your email. The recipient only gets access to the files you choose.

Problem: Errors that include "blocked" or "listed in" and references to sites like "spamcop," "dynablock," "blackhole," or "spamhaus."

Explanation: Your message is intentionally blocked by a blacklist filter because the recipient’s service provider thinks the mail server you're using is a source of spam.

Try this fix: Contact the support team of recipient's email provider and request to have your account or domain unblocked.