Email Delivery Errors

It’s never fun to see an email bounce back to you with an error!

We’ve made this guide to help you identify and understand seven of the most common errors you will see and the next best step to fixing each problem.

Incorrect Email Address

• “The email account that you tried to reach does not exist”
• “Requested action not taken: Mailbox unavailable”
• “Not a valid recipient”

This error typically happens when the email address you used in your message was mistyped or the person who originally gave you that address made a mistake. Double check to make sure you’re spelling it correctly and that there are no spaces or characters that shouldn’t be there, then try again.

If your message fails with an invalid address error again, refrain from sending more to this person until you can acquire the correct address. The more an email server sees failed attempts like this, the higher the chance it may think you are a spammer.

Mailbox is Full

• “The email account you tried to reach is over quota”
• “Mailbox full”

When someone has maxed out the capacity for their email account or bundled file storage, no more messages can be sent to that account until space is freed back up. You’ll want to contact them through other means to let them know about the issue so they can get everything working normally again.

Address Blocked by Recipient

• “Marked your email as spam and is currently blocked”

If you see a message like this, it suggests that your emails have been blocked either by the recipient (manually) or their email server (automatically) because something about your mail seems unsolicited.

If you think this is a mistake, reach out to the recipient through other means to let them know your messages are legitimate. If you continue to have these problems or spot it happening with multiple recipients, consider how you format your emails (including the words and content you include), as there may be something in them that is accidentally tripping spam filters.

Domain on Block List

• “Our system has detected that this message is suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked”
• “Service unavailable, MailFrom domain is listed in Spamhaus”

Email deliverability is strongly tied to how reputable your domain is, so getting your email addresses blocked repeatedly could harm that reputation.

It’s a best practice to handle the instructions above for “Address Blocked by Recipient” whenever possible to ensure any misunderstandings don’t stick to your domain itself.

DMARC Policy

• “Unauthenticated email from example.com is not accepted due to domain's DMARC policy”
• “Message rejected due to DMARC”
• “Email rejected per sender's DMARC policy” 

DMARC stands for “Domain-based Message Authentication, Reporting, and Conformance.” It’s basically a protocol to ensure that emails are definitely being sent from the accounts they claim to be, to prevent fake addresses from being used or people being able to impersonate other people or businesses.

So, why does this problem happen and how do you fix it? The vast majority of the time, it’s caused by the next two following error situations, so troubleshoot those and you will likely fix whatever is invalidating your DMARC policy:

SPF Error

• “550 SPF check failed”
• “spf too many dns lookups”
• “SPF Temperror” (or “Permerror”)

Sender Policy Framework (SPF) is a security protocol that verifies if an email is legitimate by confirming that the IP it’s being sent from is indeed allowed to send it.

If you are seeing these errors, you will need to reach out to your domain provider and ask them to check your domain’s SPF record for issues that could be causing mismatches between IPs and your domain’s DNS.

DKIM Error

• “crypto/rsa: verification error”
• “dkim=fail”
• “dkim=temperror” (or “permerror”)

DomainKeys Identified Mail (DKIM) verifies email integrity using cryptographic signatures to make sure that an email is truly being sent from the domain the sender is claiming.

Just like an SPF error, if you are seeing a DKIM error, you will want to contact your domain provider and ask them to check your domain’s DKIM record for syntax problems and to make sure your DNS is not experiencing downtime.