Question: There's a PM stuck in my Outbox. What's wrong?
This behavior is confusing but normal. When a PM is "sent", it goes simultaneously to the sender's Outbox and the recipient's Inbox. The PM will remain in the sender's Outbox until the recipient logs in and reads the message. At that time, on the sender's side the message will magically migrate from Outbox to Sentbox. You can think of it as a somewhat bizarre form of read receipt.
So, the message that appears stuck in your Outbox just means that your recipient has not read the PM you sent.
In most cases the forum software will also send a notification email to the recipient of a PM, to notify them that a PM is waiting. But some people turn off that notification. In cases where a PM goes unread for a long time, it's probably a good idea to send an email through the forum also. That will work unless the recipient has specified a non-working email address, which also happens from time to time.
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