Some sent emails are stuck in OUtbox of Outlook.com android mobile app

The problem is very likely your oldest message in your Outlook-for-Android app's Outbox.  In my case, my FOUR oldest messages were each problems.  I began by deleting them one at a time, the oldest one first.  Following each individual deletion, I returned to the Inbox, and clicked the Sync button.  Upon syncing after the fourth oldest one was deleted, more than entire month worth of email messages that had been jammed up in my Outbox without me realizing it all got sent in a long, multi-minute sync-up.

NOTE TO MICROSOFT:  Made the Outlook-for-Android app somehow prominently display that their are unsent messages in the Outbox, like a pop-up that has to be "OK'd", rather than having to open the drop-down list of folders to see the Outbox, at which time I am usually on my way to a specific folder, and immediately start scrolling without even noticing that their are one or more messages indicated in the Outbox.

Hotmail's individual email message attachment size limit is still 10MB, I believe--has been for many years.  All of the messages blocking my Outlook-for-Android app's Outbox were less than 10MB (Hotmail, itself, as opposed to the Outlook app, had given me an error when I tried sending them together as one email message, so I broke them up into four separate messages).  So, I don't think the problem had anything to do with size of the attachments.  Maybe the problem had something to do with the fact that they had attachments, at all, however, and maybe not--personally, I don't think so.  What I am pretty certain the problem had to do with was my connection status when I tried sending the messages.

All four of them were attempted sends from the same physical location at approximately the same time.  At that time, I was vacationing in a location that was not serviced by my carrier, and although my voice service was roaming, roaming was not available for data service unless I paid for it (T-Mobile in Montana), which I didn't, so I only had a data connection if and when I was connected to Wi-Fi.  I don't believe I had turned off my phone's mobile data radio, however, so I believe my phone (an LG Nexus 4) was making attempts to link up to data towers, and I believe my phone was in some sort of limbo or error state between the Wi-Fi radio and the mobile data radio when I attempted to send the emails (I believe all email activity is via data connections, but even if not, these four messages would definitely have required a data connection, due to the images I had attached to them).  I believe this limbo or error state caused some sort of malfunction that either Android or the Outlook app wasn't able to rectify, even after an eventual data connection was established.

This whole process created a bit of a headache for me, as I didn't know whether recipients would receive them in their Inbox as current ("Today's") receipts, or whether they would be placed in their Inboxes chronologically by the date I originally created them and tried sending them, in which case the recipient may never even notice them being received--except for them showing as "Unread" messages, I suppose.  In my "Sent" folder, they displayed as though they had been sent on the date I created and first tried sending them.  It turns out that the messages were received by recipients the same way--as if they had been received the dates I had created and originally attempted sending them.  Many people were unaware of their existence, therefore, and so I sent follow-up duplicates with an explanatory note included.

Thanks for your help with this problem. I discovered today that two weeks worth of my emails had not been sent. It caused some real problems at work. I have downgraded my rating of the Outlook App to 1 star as a result of this problem and the general slowness and clunkiness of the app. Sad that Hot mail worked better than this. If Microsoft can't put out a better android app for Outlook I may move to gmail for all my work.

Removing your account also loses the messages in your Outbox. But that has the same end result of allowing subsequent email to actually be sent--removes the plug.

My first "stuck" email had an attachment and I suspect it didn't finish sending before my phone was turned off.

The biggest problem for me is there is no notification that this has happened. I only noticed email wasn't being sent when an important email did not get sent and my supervisor sent me "You have failed to send in the required information" type email this morning when I was SURE I had sent it . . .

THANK YOU SO MUCH FOR GIVING ME A WORKAROUND. I WAS ABOUT TO ABANDON OUTLOOK MOBILE.

I hope this is fixed before it gets me into bigger trouble :(

Brilliant... Someone who knows what they are talking about... Thank You.   PG