You've crafted the perfect email and you're ready to send it to all your subscribers. But, it comes back as failed from some recipients. Everything was right on your end: it was optimized to avoid spam filters and you've only sent to opted-in recipients — so, what went wrong?
When emails fail, there can be several reasons why. Today, we'll cover the top reasons why your email may fail and, it's likely not your fault.
The email address doesn't exist
One of the common reasons why an email will be reported as failed is because the email address being sent to doesn't exist. Maybe a recipient put in a fake email or made a typo. Either way, if the address doesn't exist, it can't be sent to.
Space in the email address
Although this may not be a typo, a space in an email address can cause an email to fail. Most email providers prevent users from adding a space to their email address for this exact reason: it makes sending very unreliable. However, some custom domains may allow spaces, which will affect your emails. Any spaces or misspellings in an email will count as a hard bounce.
The email content creates too large of a file
This one is pretty straightforward. If your email is too big, the server you're sending to may reject it. Be sure to keep emails under 15KB. To help with email size, don't use Base 64 encoded images and be sure that you're not using raw image data.
Picked up by the spam filter
Although you may have made your email so to not be picked up by spam filters, some of them may have higher protocols than others. If an email is delivered straight to a spam filter, it won't be received by the client and will show as failed as a result.
Mail server is down
If the server you are sending to is down, your email will not be received by those on that server. If the connection there is down, it will likely be fixed by the time you send your next email.
Mail server doesn't exist
This is common on custom domains. If the MX records are missing, the system won't be able to tell what the server is and will take its best guess at how to send emails to it. If the system correctly guesses, your email will be sent but if the guess is incorrect the email will fail and will be a hard bounce.
Mail server rejects email
This one doesn't happen very often, but if someone has custom rules set up on their mail server, it can cause the server to reject your email.
The server is busy
If a server is busy, the system will retry to send your email 10 times. If the server is busy for all of those retries, the send is reported as a fail.
Server is over quota
If the server is full and cannot receive any new emails, the send will fail. This often happens when people go away or are on vacation and don't check/delete emails for an extended period of time.
Writebacks are backed up
This reason is specific to systems like SimplyCast where you can view your reports in an email dashboard. Essentially, if a campaign is saying that it hasn't sent, it may not be accurate if you're looking at it immediately after it sends. This is because of the way reporting is generated for each campaign. Once the email is sent, it sends a response to the server. This response is added to a queue to be written back to reports. So, if there are a lot of send responses waiting in the queue, it may take a while to generate all the reports. This typically only happens when a lot of people are sending large campaigns. However, open rates are not written back in the same fashion as sends so it is possible that you may see opens before you see sends.
Do you have any other questions about email sends and fails? Let us know in the comments below.