The emails I send are undeliverable because they have been marked spam. How do I mark them as safe?

Question

The emails I send are undeliverable because they have been marked spam. How do I mark them as safe?

Librarian 0

I send out a daily newsletter to a dozen friends. Hotmail has decided these are spam so they now bounce back as undeliverable. How do I fix this?

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2 answers

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Answer 1

EmilyS726 271.5K Independent Advisor

You cannot mark your own outgoing messages as “safe.” The Safe Senders list controls incoming mail at the recipient’s mailbox.

However, if the messages are actually bouncing as undeliverable, rather than merely going to Junk, the important information is the error code in the non-delivery report. A recipient adding you as a Safe Sender may not help if the message is being rejected at the server level.

Sending a daily newsletter-style email to a dozen recipients does run the risk of triggering anti-spam filtering.

Can you please share the complete bounce-back message to see if it might provide information for the exact reason? Feel free to redact any personal information before posting it.

Librarian 0 Reputation points

2026-09-05T18:13:57.23+00:00

Diagnostic information for administrators:

Generating server: BY3PR05MB8921.namprd05.prod.outlook.com

******@gmail.com Remote server returned '554 5.7.0 < #5.7.520 smtp;550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)>'
EmilyS726 271.5K Reputation points Independent Advisor

2026-09-05T18:23:03.71+00:00

Thank you.

This definitely confirms that the block is from the anti-spam filter on the server side.

Given that this is a daily newsletter-style message sent repeatedly to a group of recipients, the pattern and/or something in the message content is likely triggering the filter.

Next step is to narrow down and see if it is content-related or account-reputation-related.

Can you use the instruction here, change the email to plain text or rich text format (basically avoid the html format), send a test email with one liner "This is a test email", also don't include signature or URL. Let me know if it goes through.

https://support.microsoft.com/office/change-the-message-format-to-html-rich-text-format-or-plain-text-in-outlook-338a389d-11da-47fe-b693-cf41f792fefa
Librarian 0 Reputation points

2026-09-05T18:45:28.1433333+00:00

I sent a generic test email to one individual using plain text. It went through.

I tried to send a newsletter with plain text, it did not go through.
EmilyS726 271.5K Reputation points Independent Advisor

2026-09-05T18:46:45.3733333+00:00

Did you send the newsletter to one user or multiple?
Librarian 0 Reputation points

2026-09-05T18:47:59.5566667+00:00

multiple
EmilyS726 271.5K Reputation points Independent Advisor

2026-09-05T19:24:35.25+00:00

Do you mind trying just one?

Right now we can narrow down that this is not account/IP address reputation issue.

It can still be due to content issues and/or a "mass sending" issue.
Librarian 0 Reputation points

2026-09-05T19:37:40.83+00:00

I sent the newsletter plain text to one person. It bounced back as undeliverable.
EmilyS726 271.5K Reputation points Independent Advisor

2026-09-05T19:45:36+00:00

Thank you. So that means the content itself is the problem.

Microsoft's anti-spam filter can be quite dynamic. It can become stricter if overall (not limited to your account) spam activities are high.

Things that can increase the likelihood of being flagged include repetitive newsletter-style wording, many short promotional statements, excessive capitalization or punctuation, phrases such as “click here,” “limited time,” “free,” “act now,” repeated URLs, phone numbers or contact details, and sending essentially the same message every day.

I would suggest testing a more natural, conversational rewrite of the newsletter while keeping the same information. If the rewritten version succeeds, that would strongly indicate the content/style pattern is contributing to the filter.
Librarian 0 Reputation points

2026-09-05T19:49:50.4266667+00:00

Thank you for your time and help.
EmilyS726 271.5K Reputation points Independent Advisor

2026-09-05T19:50:37.21+00:00

You are welcome.

Answer 2

For Outlook.com, sent messages cannot be manually marked as safe. The practical fixes are to reduce the chance that Outlook.com classifies the message as spam and ask recipients to trust the sender.

Try these steps:

Check message content.
- Remove anything that looks spam-like.
- Avoid excessive links, URL shorteners, embedded scripts, image-only content, and heavy formatting.
- Send a plain-text test message first.
Change sending behavior.
- Do not put all recipients in BCC.
- Reduce sending volume or frequency if possible.
- Avoid sending to people who never read or reply.
- Add a clear sender name so the message is easily identifiable.
Build sender trust.
- Send an email to the same account and reply to it.
- Add recipients to Contacts.
- Ask each recipient to mark the message as Not junk and add the address to their Safe senders list.
If a recipient uses Outlook.com and a message lands in Junk, they can fix it by:
- Opening Junk Email.
- Selecting the message.
- Choosing It’s not junk.
- Adding the sender to Safe senders and domains.
If messages are already bouncing with spam-related blocking, simplify the newsletter and resend a test version with no links or attachments.

If the issue is specifically with Outlook.com or Hotmail recipients, Microsoft also recommends checking whether antivirus software has Internet Email Auto Protect or Internet Email Protection enabled and disabling that setting before testing again.