Dear Audrey Leonard,
Thanks for using Microsoft products and posting in the forums!
It sounds like you're experiencing issues with sending or replying to emails using Outlook on your iPhone.
In order to help you more efficiently, the following information needs to be gathered with you:
1, Did this problem happen suddenly?
2, What domain name are you using for your email?
3, Can you send and receive emails on webmail?
When you are using a Microsoft domain email, if this problem occurs with Outlook for iPhone, I suggest you first go to webmail outlook.live.com through a browser, to check if you can send/receive emails there. The purpose of doing this option is to eliminate as many interruptions as possible, webmail synchronization is fast and good, so that you can easily figure out whether the problem is with the email account or with the outlook app itself.
If you can send and receive emails on webmail normally, your email account is fine.
The problem must be in iPhone, you can try the following methods to troubleshoot the problem:
Restart iPhone: Sometimes, restarting your iPhone can resolve temporary network or email issues. Turn your iPhone off and then back on.
Check for iOS Updates/Outlook app: Make sure your iPhone is running the latest version of iOS. Outdated software can sometimes cause email problems. Go to Settings > General > Software Update to check for updates and install any available updates. It's okay to just delete Outlook app and then install it from the Apple Store.
Remove and reconfigure your Outlook email account on your iPhone:
Go to Settings > Mail > Accounts.
Select your Outlook email account and choose Delete Account.
Once deleted, add the account again by selecting Add Account and following the on-screen instructions.
Please feel free to share more and let me know if you need further assistance.
Best regards,
Harris-MSFT |Microsoft Community support specialist