"The sender address was invalid" error when I attempt to send an email.

This happened suddenly without me apparently updating anything in my settings. My laptop sent emails easily and one of my other email addresses worked.

go to Settings>Mail>Your email account>Outgoing mail server>got to the server. my username and password were populated with 'optional'. I entered my email address and the password for that email address.

This immediately fixed the problem. (I have never ever touched those settings before in my life!!!!)

That error is from your email provider; you need to contact them to resolve the problem. It might be the result of you not having a valid user ID and password for the outgoing mail server (the SMTP server). Go to Settings/Mail/Accounts, tap on the account, then the outgoing server settings.

Happened to me also,

tried: Settings>Mail>Your email account>Outgoing mail server>got to the server. my username and password were populated with 'optional'. I entered my email address and the password for that email address.

Problem fixed!!

I have had the same problem and went in my Spectrum email and took out my password under my email and

it now works ok. I have been working on finding this problem for three days.

The password is the one on the server given me when I set up my original email address.

Thank you for this solution. I had the same issue and this worked. I am getting SO fed up with Register.com. Years ago when I setup my email with them, I thought it would be so cool to have an email with my own domain name. But at least once a year I seem to have an issue with my emails working on my Apple devices, and it's usually something like this, where Register.com changes some setting and doesn't tell you. Then you have to waste time trying to fix it. I have NO such issues with my other emails via gmail. But because this is my main email, and I use ALL over the place, and have for years, it would be a real pain to change it now. So again, thank you!

I am having the same problem with my local server, gmail and yahoo. All of them say invalid email address when replying to an email. Didn't have this problem until updated to 17.4. Now have 17.4.1 with the same issue.

This advice was spot on. Register.com didn't want to tell me. They said they can forwarded me to an advance tech support for a fee. I said no thanks, went online and found the answer above. Thanks.

I just switch to iphone 11 to 15, didn't do anything. It automatically bluetooth/ transferred the information from my old phone to the next one. I guess new phone, add a password.

I followed the directions given above, however my phone won’t let me fill in username nor password. They both have optional but won’t let me change them

Sender address was invalid after sending email

Had the same problem after doing a software update on my Apple Watch??

I followed the same actions as recommended and problem was solved

I did have this problem after a recent update 17.4.1

I followed the instructions as well but won't let me change password from optional and still won't work.

Thanks. This worked a treat for me for an imap account hosted by IONOS

This has been frustrating me for weeks. Now fixed. THANKYOU

Sender address invalid: how fix