How to fix blank SMTP settings preventing email sending on iPhone?

Hi,

This issue is almost certainly related to the outgoing (SMTP) mail server configuration rather than the Mail app itself.

What likely happened:

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• The large attachment caused the message to get stuck in the outgoing queue
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• When the message was deleted, the SMTP configuration for that account either became inactive or lost its association
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• That’s why you can receive mail and send from other accounts, but not from this one
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Here’s what to check step by step:

1. Verify SMTP settings (most important)

Go to:

Mail → Settings → Accounts → [affected account] → Server Settings

Under Outgoing Mail Server (SMTP):

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• Make sure a server is selected (not blank)
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• If it says “None” or is empty, click Edit SMTP Server List
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• Select the correct SMTP server or add it again
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Typical SMTP settings (example):

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• Server name: smtp.yourprovider.com
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• Port: 587
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• Use TLS/SSL: On
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• Authentication: Password
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• Username: full email address
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• Password: email password (not app password unless required)
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2. Disable “Automatically manage connection settings”

Sometimes Apple Mail fails to repopulate settings correctly.

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• Turn off “Automatically manage connection settings”
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• Re-enter the SMTP details manually
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• Save and restart Mail
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3. Remove stuck outgoing messages

Even if Outbox looks empty:

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• Quit Mail
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• Reopen Mail while holding Shift
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• Check Window → Connection Doctor and ensure SMTP shows green
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4. Test with a new message (no attachment)

Send a short plain-text email to yourself.

If that works, the issue was definitely SMTP-related.

5. If still broken: re-add only the SMTP server

You usually do not need to remove the whole account.

Just deleting and re-adding the outgoing server is often enough.

Important tip

Avoid retrying large attachments in Apple Mail until SMTP is confirmed working. Repeated failures can cause Mail to silently disable the outgoing server.

If you want, I can also:

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• Adapt this answer to Gmail / iCloud / Outlook specifically
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• Make a shorter version for Apple Community style
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• Help you phrase a follow-up reply if someone asks for details
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Just tell me 👍

[Edited by Moderator]

To send large files, use iCloud: Share files and folders in iCloud Drive on iCloud.com - Apple Support

For your email, ensure that large-attachment message is not still stuck in your outbox mailbox. If still in the outbox, delete it.

To get the mail account working again, test with the webmail access into your mail. This checks the credentials.

Then check whether sufficient storage quota is available on your mail server. How to do this varies by mail server. With iCloud, here is how: Check your iCloud storage on any device - Apple Support

Then next delete the mail account entirely, and re-add it. Removing and re-adding is what Apple recommends, and usually clears these issues, and it is usually both the easiest and fastest fix. Removing the account does not affect mail stored on the server, or mail stored locally.

The remove-and-re-add is at the bottom of this: If you can’t send or receive email on Mac - Apple Support