email disappears after you reply to original

Why does she need to listen and erase her whole phone when she already told you that is NOT the problem. She’s talking about the way Mail threads incoming and outgoing mails into a single thread…

For gmail accounts see the article https://support.google.com/mail/answer/7015314?hl=en-GB&co=GENIE.Platform%3DiOS&oco=1#zippy=%2Ccheck-whether-your-emails-are-being-forwarded-to-another-account

Check whether your emails are being forwarded to another account 

When you set up forwarding in Gmail, you can choose whether the original emails are archived or deleted.

Here's how to check your forwarding settings:

1. From a browser, open Gmail.
2. In the top right, click Settings   See all settings.
3. At the top, click on the Forwarding and POP/IMAP tab.
4. In the 'Forwarding' section, check whether you've selected Forward a copy of incoming mail. If you have, select Keep Gmail's copy in the Inbox or Mark Gmail's copy as read.
5. At the bottom of the page, click Save changes.

Important: If your emails are being forwarded to an unfamiliar address, select Disable forwarding then take a look at the Gmail security tips. If you can see a forwarding address that you don't recognise, someone might have unauthorised access to your account.

If you forward email from another account into Gmail, emails are sometimes sent to Spam if they aren't authenticated. Learn the best practices for forwarding emails to Gmail.

The mail application is not working , delete the account and once again configure If you can't receive email on your iPhone, iPad, or iPod touch - Apple Support

Same here. The original email only appears as part of the reply, meaning attachments are inaccessible.

mine isn’t iCloud, but my own pop account. If I shut down Mail and open something else, then return - it’s back. But immediately after replying it vanishes.

bug.

Please take suggestions from apple support , you can erase the iPhone and once again configure the account and the mail application .

I have sent emails from my iphone either new ones or replying to an email thread and the email just disappears as if I have never sent it. Is there a way to fix this?