When a user with the Browser role added a subscription, it would fail when sending an email.

I recently had this issue with SSRS Subscriptions in SQL 2008 R2. My initial search landed me in an MSDN article that seemed to be telling me:

If you are using an SMTP server or forwarder that uses e-mail accounts that are different from the domain user account, the report delivery will fail when the SMTP server tries to deliver the report to that user.

Based on this, I submitted this information to our network guys to make sure this wasn't the issue (as I don't manager our mail server). However, I continued to search for a solution because the above reason didn't really seem like it was the actual issue.

Then, as I read on down the article, I saw set number 3 in the section where I pulled the comment from above. It made me think that maybe if I set the DefaultHostName property to our domain name then it might fix the issue. Voilà the subscriptions started working!

Shortened version of the steps:

1. On your SSRS R2 server open: "C:\Program Files\Microsoft SQL Server\MSRS10_50.MSSQLSERVER\Reporting Services\ReportServer\rsreportserver.config"
2. Find the property:  DefaultHostName
3. Add your domain name in that property.