It looks like Apple has introduced a new 15MB limit for the SMS mailbox in iOS 5. So if you exceed this limit then you won’t be able to receive new messages and will get the following error message:
“Your SMS mailbox is full. New messages cannot be received until you delete some messages.”
Apple reveals this new limit in the knowledge base article that was published on October 15th. It reads:
iOS messaging database is limited to 15 MB of storage, which is about 75,000 messages. If you have updated and your iPhone displays the following message:
Apple has provided the following solution to fix the issue (which is not an ideal solution if you ask us):
- Delete message conversation threads by swiping left or right over a conversation and tapping Delete.
- Restart your iPhone.
It is not clear why Apple has decided to limit the SMS mailbox size to only 15MB, but based on this Apple Discussion thread, it looks like quite a few users are getting the message after upgrading to iOS 5.
Let us know if you have got this error message.