False positive - 550 5.7.520 when sending from Apple Mail on iPhone

Question

False positive - 550 5.7.520 when sending from Apple Mail on iPhone

Elena Arribas 0

Hello,

I believe Outlook.com is incorrectly blocking legitimate emails as spam.

My tests are:

I can send emails normally from Outlook Web.
I can send emails from Apple Mail on my iPhone to Yahoo and corporate email addresses.
Emails sent from Apple Mail on my iPhone to my own Hotmail address or my Gmail address are rejected with:

550 5.7.520 Message blocked because it contains content identified as spam.

The message is a simple plain text email (for example, just "Hello"), with no attachments or links.

I have already removed and re-added the Outlook account on my iPhone.

This appears to be a false positive in the Outlook.com outbound spam filter affecting messages sent from Apple Mail for iOS.

Could you please investigate this issue?

Thank you.

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1 answer

Your answer

Answer 1

Hello

Emails sent from phone apps are not in plain text format. I understand that you only sent a word like "hello", but that's not the definition of plain text. By default, emails sent from mobile app is html format, meaning, behind the scene, your "hello" carries tags in the raw code. As far as I know, there's no way to switch it to plain texts with the app. On the web or desktop app you can do so.

Issue like this should be temporary. In the email industry, each sending IP address carries a reputation score. That score is influenced by how much spam or abusive activity is associated with that IP address or its broader IP range. If too much abuse is detected, the reputation drops. When it falls too low, other email providers may start rejecting messages coming from that range.

To address the problem and restore the IP reputation, the email service provider usually has to tighten its outbound spam filtering. Since a large volume of spam is sent in HTML format, messages sent as HTML are often more likely to be caught under these stricter filters. Once the IP reputation improves, the filtering is typically relaxed again.