Some iPhone users and iPod touch users may find that they occasionally can’t send an e-mail message, even though they’re receiving messages just fine. Here are three of the most common culprits.
If you accidentally drag a message from your Inbox to your Outbox, the iPhone can’t identify the message’s sender and will show an error. You might think you just need to take the offending message out of the Outbox. However, Apple reports that once this error appears, the e-mail message may become invisible.
To make it reappear, you must turn on the iPhone’s Airplane Mode or turn off the iPod touch’s Wi-Fi. This should trigger the reappearance of the MIA message, allowing you to delete it.
Yahoo Mail problems
Are you only having problems with your Yahoo! Mail account? If your iPhone is showing the error “Connections to the outgoing servers ‘(null)’ failed,” you’ll likely need to wait for Yahoo to update its mobile e-mail software. In this case, the iPhone is typically not to blame.
One troublesome account
If you are having other problems sending e-mail from a given account, your best bet is to delete the problematic account and create a new one. When doing so, use the “manual” settings—accessed by tapping “Other” when you go to Settings -> Mail -> Add Account—rather than one of the default settings that may be available.
Bonus bug: iPhone Unknown error (6)
While we're on the subject of the iPhone, let's tackle the issue of an not very illustrative error message. If you try to make a fresh start with you phone by using iTunes to restore your iPhone to factory settings, you might get the error “Unable to restore iPhone. Unknown error (6).” If so, update to the latest version of iTunes.
If that doesn’t fix the problem, the most likely cause is that one or more of the .ipsw files, located in your user folder/Library/iTunes/iPhone Software Updates folder, are damaged. The solution is to delete the files and try the Restore command again. New copies of the files will download and the process should proceed as expected.
This article was reposted at 1:35 p.m. to correct an error in the User error section.