If an external sender (such as an automated service, SaaS application, or business partner) reports that emails sent to your domain are bouncing back with an error like
554 5.7.1 Service unavailable; Client host [IP] blocked using bl.spamcop.net, your mail server is rejecting traffic from a flagged sender IP address.This occurs when the sending company's email server IP address is listed on a global DNS Blocklist (DNSBL) such as SpamCop, Spamhaus, or Sorbs.
Understanding the Bounce Error
When an external sender tries to deliver an email to your mailbox hosted on Plesk, our mail server performs an automated security lookup against global threat intelligence databases:
Sender Server (e.g., Sprout Social / Amazon SES)
│
▼
Incoming Mail Server (Plesk Server)
│
├──► Checks SpamCop/DNSBL Database
│
└──► RESULT: Sender IP is listed on SpamCop ──► Mail REJECTED (554 5.7.1)
Common Error Messages Received by Senders:
554 5.7.1 Service unavailable; Client host [54.240.x.x] blocked using bl.spamcop.net
550 5.7.1 Command rejected: Mail server IP is listed on bl.spamcop.net
554 5.7.1 Message rejected: sender IP blacklisted
Step-by-Step Resolution Process
Because the block is triggered by the sender's server reputation rather than your domain settings, resolving the issue involves actions by both the sender and your hosting team.
Step 1: Actions Required by the Sending Organization
- Notify the Sender: Inform the sending company (or their technical support) that their outbound sending IP address is listed on SpamCop or another DNSBL.
- Request Delisting: The sending provider must clean their outbound mail queue and submit a delisting request directly to SpamCop or the relevant blocklist operator.
- Temporary Bypass (If Applicable): For critical one-time passcodes or authentication emails, request that the sending service temporarily bypass or send via an alternate channel while their IP reputation is restored.
Step 2: What Our Support Team Can Do for Your Plesk Account
If you need to receive emails from the flagged sender immediately, our support team can inspect server logs and configure an IP-level exemption on the mail server.
Please contact Support with the following details:
- Recipient Mailbox: The full email address on your domain attempting to receive the message (e.g.,
user@yourdomain.com).
- Sender Email / Domain: The email address or domain of the sender (e.g.,
noreply@service.com).
- Sender IP Address (If known): Found in the bounce-back report (e.g.,
54.240.9.36).
- Approximate Timestamps: Date and time window when the email or passcode was requested.
Technical Actions We Take on Plesk
When you submit these details, our hosting administrators will:
- Inspect the Plesk server mail logs (
/var/log/maillog) to confirm the rejected connection attempts.
- Add the sender's sending IP address directly to the Plesk Mail Server Whitelist.
- Allow legitimate business emails from that specific server to bypass DNSBL rejections safely without lowering overall anti-spam protections.
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