Outbound email blocked — error 550 5.7.520 AS(4810) — all recipients including Hotmail

Question

All outbound emails are getting blocked. This affects all recipients across all domains. I send to groups frequently and this is new behavior. I've been using this account daily for 25+ years.

Answer 1

Hello

Is that the entire bounce back message? Typically there's more information in that email. Do you mind sharing the entire email minus the reference of any email addresses?

Answer 2

Error 550 5.7.520 indicates that outbound mail is being blocked because the sending account, IP, or domain is being treated as a spam source or is on a blocklist.

For Outlook.com/consumer accounts, the most common causes and actions are:

1. The sending account or server has been flagged as a spam source
   • Recipient systems (including Hotmail/Outlook.com and others) may be using spam or blacklist filters (for example, Spamhaus, Spamcop, etc.) that have listed the sending service.
   • This can happen even if the account has been used legitimately for many years, especially if:
     • A large number of recipients are in groups/lists.
     • A message resembles bulk or marketing email.
     • The account was compromised and used to send spam.
2. What to do next
   • Review any “delivery failed”/NDR messages for wording such as “blocked,” “listed in,” or references to blacklist providers (for example, spamcop, dynablock, blackhole, spamhaus). This confirms that a spam/blacklist filter is blocking the mail.
   • Contact the support team or postmaster for the recipient’s email provider (or, if all domains are affected, the provider that hosts the sending account) and request that the account or domain be unblocked.
   • If the error mentions a blocked IP, follow the provider’s delisting process or self-service delist portal if available.
   • Ensure that:
     • No one else has access to the account.
     • There are no signs of compromise (unexpected sent items, unfamiliar rules, etc.).
3. If the error is due to a custom blocklist
   • Some recipient domains maintain their own custom blocklists. In that case, only the recipient’s administrator can remove the sending IP or address from their list.
   • The sender must contact the recipient (for example, via another email address or channel) and ask their admin to remove the block.

Because this affects all recipients and started suddenly, it is very likely a reputation/blocklist issue and requires contacting the relevant provider(s) to remove the block.

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References:

• Sent email in Outlook.com comes back "delivery failed"
• Email non-delivery reports and SMTP errors in Exchange Online