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The purpose is to let you know that we received an email we could not process. On the chance that you might have an email client that does open the email we attach it to the message. 

 Is there a file size limit to the emails I receive and sent through Actionstep?

When sending emails out of Actionstep there is a limit of 50Mb per email. If an email and/or its attachments exceed 50Mb the user will receive an error message. If you are often sending large attachments consider using the Actionstep Portal as an alternative. 

There is no limit to the size of emails that are received into Actionstep though there is likely to be a limit set by the mailbox that you have Actionstep set to pull from.