Emails sent out ar coming back as undeliverable. It mentions could be spam in the description

The behavior matches Outlook.com treating the messages as potential spam or hitting sending limits, especially with a large Bcc list and frequent bulk sends.

Use these steps to restore sending and work around the limits:

1. Check the non‑delivery report (NDR)

• Open one of the “Undeliverable” messages and read the detailed error text.
• If it mentions “blocked,” “listed in,” or references sites like “spamcop,” “spamhaus,” etc., the account or sending IP is being blocked by spam/blacklist filters on recipients’ servers.
• If it mentions “Message too large,” “Mailbox full,” “Host unknown,” or similar, follow the specific guidance below.

2. Reduce spam‑like characteristics

• Avoid sending to very large groups in a single message. Even though 200 recipients is below some hard limits, it can still trigger spam filters.
• Continue splitting the list, but:
  • Send to smaller batches (for example 20–30 recipients per message).
  • Space out the sends over time instead of sending all batches at once.
• Avoid subject/body text that looks like mass marketing or spam; keep the wording simple and personal.
• Make sure all recipients are legitimate contacts who expect the email.

3. Check Outlook.com sending limits and reputation

• New or recently upgraded Outlook.com accounts can have low sending quotas that increase over time. If the account was recently created or upgraded, it may still be restricted. See “Sending limits in Outlook.com” from the context for details.
• If a non‑delivery receipt is received and the recipient address is correct, use the dedicated support channel: go to “Sender Support in Outlook.com” (linked in the context) and follow the steps there to request review/unblock of the account.

4. Verify recipient addresses and list quality

• Make sure all addresses in the group are valid and current. Common NDR reasons include:
  • Invalid email address / Mailbox not found / User unknown.
  • Host unknown or Domain lookup failed (domain no longer exists or is misspelled).
  • Mailbox full or Quota exceeded.
• Remove any addresses that consistently bounce with these errors.

5. Check for “Message too large” or attachment issues

• If any message includes attachments, ensure the total size is well under Outlook.com’s 25 MB limit per message.
• If large files are needed, upload them to OneDrive and send a sharing link instead of attaching them directly.

6. If NDR mentions spam/blacklist explicitly

• When the error text includes “blocked” or “listed in” with references to blacklist services (for example “spamcop,” “spamhaus”), this indicates intentional blocking by the recipient’s server.
• In that case, contact the support team for the recipient’s email provider (or ask one of the affected recipients to contact their provider) and request that the account or domain be unblocked.

7. Try sending from Outlook.com web directly

• If using an email app (desktop Outlook, mobile app, etc.), sign in to Outlook.com in a browser and send a small test message (for example to 3–5 recipients).
• If the web send works but the app does not, the issue may be with the app configuration; re‑add the account in the app.

8. When nothing goes through (even to 3 recipients)

• This strongly suggests a sending restriction or reputation block on the Outlook.com account itself, not just a recipient limit.
• In that case, prioritize:
  • Cleaning the list (remove invalid/bouncing addresses).
  • Reducing batch size and frequency.
  • Using “Sender Support in Outlook.com” to request investigation and removal of any sending block.

References:

• Can't send or receive email in Outlook.com
• Sent email in Outlook.com comes back "delivery failed"
• Failed delivery messages from the postmaster at outlook.com, microsoft.com, or service.microsoft.com