Why is my suppression list upload showing an error?

You encountered an error when uploading a file you wish to suppress from an upcoming campaign, "The file uploaded cannot be processed."

This article will walk through common troubleshooting steps.

File Setup Checklist

1. File format is .txt.
2. File contains email addresses only, no names or other data is present.
3. The email addresses are listed one per line and there are no commas or other characters used to separate the listed email addresses.
4. There is not a header row present in the file like "Email" or "Email Address" that may have been brought over from a copy & paste function. 
5. There are no other header rows present.
6. There are no empty rows at the top or bottom of list. For instance, there is not a blank row above the list of emails in the file, or below the list.
7. All emails appear to be in a proper format.

Additional items to look for as last resort

1. Are any of the email addresses in all caps? Try changing to lower case if so.
2. Are you using a Mac? Double check that the file was actually saved as plain text. If you're not able to verify this, you can copy the list of emails into an excel worksheet. Then save it as "Tab delimited Text version". This will make sure it's in the right .txt format. 

When all else fails, there are alternatives to suppression files

1. Use the suppress segment or category feature in the Campaign instead of using an uploaded suppression file. To do this, import your list of email addresses into your account and create a new category. In step 3 of the Campaign setup (Contacts) choose to suppress by category. OR
2. After creating a category as indicated above, update the segment or category that you intend to send the Campaign to with a clause "not in" category.