Outlook.com Says "We Couldn't Send Your Message"? How to Fix Sending

You can receive mail in Outlook.com but sending fails — you get “We couldn’t send your message” or the message just won’t leave.

Why receiving works but sending doesn’t: the most common causes are account- or quota-related rather than a connection problem — a full mailbox/storage, a sending limit on a newer account, a temporary block after unusual activity, or even a signature the system chokes on. Recipient-side problems (full mailbox, spam filtering) can also bounce a message back. This covers the Outlook.com website/account; the new Outlook for Windows app shows similar errors for the same reasons.

Fix 1: Check your storage and the message size

1. If your Microsoft cloud storage is full, you can’t send or receive — check what’s using it and free up space (mail, OneDrive, and photos share the quota).
2. Confirm attachments are under the limit; messages with attachments over 25 MB won’t send. Use a OneDrive link for large files instead.

Fix 2: Make sure your account isn’t blocked

1. If your password changed recently, sign in again with the current one.
2. Outlook.com temporarily blocks accounts after unusual sign-in activity. Unblock it via Microsoft’s unblock page and verify your identity.

Fix 3: Sending limits on a new account

New Outlook.com accounts start with a low daily sending limit as an anti-abuse measure. It increases automatically as the account builds a reputation. See Sending limits in Outlook.com for the current numbers — if you’ve hit it, wait and try again later.

Fix 4: Remove the signature, then resend

Signatures can sometimes block a message from sending:

1. Delete the signature from the email you’re trying to send.
2. Send the message again. If it goes through, rebuild the signature (often an oversized or broken image is the culprit).

Fix 5: Rule out the recipient

If only mail to one person fails, the issue may be on their end — a full recipient mailbox, a down mail server, or their spam filter blocking you. Confirm the address is spelled correctly and try a different recipient to isolate it.

FAQ

My message bounced back as “delivery failed.” That’s a non-delivery report — read the reason in the bounce; it usually names a bad address, a full recipient mailbox, or spam filtering.

Sending was fine yesterday and now hits a limit. A sudden send-limit block often follows a burst of messages or a security flag — wait it out, and make sure the account isn’t compromised or blocked.

Does a full mailbox really stop sending? Yes — when storage is full Outlook.com stops both sending and receiving, and incoming mail bounces to senders. Free up space first.

Sources: Microsoft Support — Can’t send or receive email in Outlook.com