The sender address was invalid. Issues on SMTP on one iPhone

Question

Level 1

4 points

The sender address was invalid. Issues on SMTP on one iPhone

Hi. I migrated my family email provider. Set up was fine, MX records altered. Incoming emails and emails sending fine from web service and Outlook. On mine and my wife's phone we access a pop3 mailbox so we both see certain emails. On both our outlooks and my iphone, they receive and send email. However, on my wife's iphone, it receives but will not send emails, with the error above.

I have checked the smtp settings and these are identical to on my phone. I have removed the email account and re-added with no change in the issue. I've added extra email accounts and thus show the same issue.

Both phones are on 18.7.1 to ensure no issues that way.

It is almost like there is an incorrect password saved somewhere but the SMTP setting is fine as when saving Apple verifies it as good with all check items. I can't see any password in password app.

Does any one have any other suggestions on where to look for a rogue password here.

Thanks

iPhone 13, iOS 18

Posted on Oct 27, 2025 10:37 AM

Reply

Answer 1

Top-ranking reply

AlWeir

Level 5

4,880 points

Oct 27, 2025 12:03 PM in response to AndyDMaxwell

Here the jist of it.

Primary Cause: SMTP Authentication Failure

The error "sender address was invalid" often means the mail server is rejecting the attempt to send an email because it cannot verify the user trying to send it.

Incorrect Password: The most common reason is an outdated or mistyped password for the Outgoing Mail Server (SMTP) settings.

Username Error: The Username for the outgoing server might be incorrect. It usually needs to be the full email address.

Authentication Method: The iPhone may be set to use an authentication method the server no longer supports (e.g., trying to use "No Password" when the server requires "Password").

Follow these steps on the affected iPhone to check and correct the settings:

Step 1: Verify Account Credentials

Go to Settings>Mail>Accounts.

Tap on the affected email account.

Tap on Account (usually at the top).

Step 2: Check Outgoing Mail Server (SMTP) Settings

Under the Outgoing Mail Server section, tap on SMTP (usually lists the Primary Server).1

Tap on the Primary Server.

Step 3: Ensure Settings are Correct

Verify the following crucial settings, which can be found on your email provider's support pages (e.g., Gmail, Outlook, Yahoo, or your company's IT):

Server: Check that the server name (e.g., https://www.google.com/search?q=smtp.example.com) is correct.

User Name: Make sure this is the full email address.

Password: Re-enter the password even if it looks correct. This often forces the phone to re-authenticate with the server.

Use SSL: This is usually ON (green).

Server Port: Verify the port number. Common secure ports are 465 or 587.

Additional Potential Issues

Reply

Answer 2

AndyDMaxwell Author

Level 1

4 points

Oct 28, 2025 1:54 AM in response to AlWeir

Thanks - but as said in my original posting - I have this working fine on PCs and my iPhone, it just does not work on my wife's phone. All the settings have been double checked between the phone that works and the iPhone that doesn't. And password re-entered and this was verified by the iPhone process. The account had been deleted and re-added with the same issue.

Reply