For an Outlook.com account that can receive but has trouble sending, check these common causes in order:
- Check whether the message is stuck in Drafts or Outbox.
- If the message has an attachment larger than 25 MB, remove it, use a smaller file, or upload it to OneDrive and send a link instead.
- Check whether the Inbox is full. If it is, empty Junk Email to free space.
- If sending from Outlook on PC or Mac with the Outlook.com account, go to Send/Receive > Send/Receive all folders.
- If Microsoft cloud storage is full, Outlook.com cannot send or receive email. Check mailbox storage and free space if needed.
- If the account password was changed recently, update it. The account can also be temporarily blocked because of unusual sign-in activity.
- If a message generates a non-delivery receipt, verify the recipient address. Common causes include an invalid address, recipient mailbox full, server issues, or spam filtering on the recipient side.
- If the account is newer or many messages were sent recently, Outlook.com may temporarily apply a lower sending quota until account credibility is established.
- If a signature is being added, remove the signature and try again.
- Add recipients to Contacts and ask them to add the address to their Safe senders list.
- Avoid sending to too many recipients at once, avoid putting all recipients in BCC, and avoid sending repeated messages to people who never read or reply.
- If antivirus software is installed, disable Internet Email Auto Protect or Internet Email Protection and test again.
If the problem is specifically with sending to Outlook.com or Hotmail recipients, improving sender reputation can help:
- send a message to the same account and reply to it
- make sure the sender name is clearly identifiable
- avoid scripting content in messages
If the issue continues, try sending the same message directly from Outlook.com in a browser. If there is a bounce-back or error code, that detail identifies the exact cause.