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If you can receive email but cannot send it, and bounces are coming back with a 550 error, your outgoing mail has been blocked. There are two different kinds of block and they need different things from you.
Check which one you have first. Read the bounce message and look at where the rejection came from.
A relay lock only affects outgoing mail. If you can still receive email normally, that confirms the problem is outbound, which rules out a lot of other causes. Worth checking before you start changing settings.

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Why outbound mail is filtered at all

On shared and reseller hosting, outgoing mail is routed through third-party filtering and relay services — MailChannels and SpamExperts. This isolates each sender, so one account sending spam does not damage the sending reputation of everyone else on the server. It is the reason your legitimate mail reaches Gmail inboxes rather than their spam folders. The trade-off is that those services will lock an account they believe is sending spam, and that lock is not something you can lift yourself.

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Relay locks

The error: 550 Your account has been locked, usually citing smtp.antispamcloud.com. This means the outbound relay has stopped your account sending, because it detected something that looks like spam or a policy violation.

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What you need to do

The lock is not cleared by waiting, and it cannot be cleared from your control panel. Three things are needed:
  1. Run an antivirus scan on the computer that sends from the affected mailbox.
  2. Change the mailbox password — see Managing e-mail accounts in cPanel. Also change your control panel password if you suspect a compromise.
  3. Open a support ticket confirming you have done both, and ask for the relay lock to be removed.
We have to investigate and lift the restriction manually. Telling us up front that the device is scanned and the password rotated is what lets us clear it quickly — without that, the first reply you get will be asking for it.
A lock can take out more than one mailbox. SpamExperts locks the sending identity, so spam detected on a single mailbox can stop the whole domain sending, including colleagues who have done nothing wrong.

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What triggers a relay lock

  • A compromised mailbox or website sending without your knowledge. This is the most common cause, and the reason the password change and malware scan are not optional
  • An application sending bursts of automated notifications. Legitimate traffic still trips the limits if it arrives in spikes
  • Links in your messages appearing on a URL blocklist such as Spamhaus, Invaluement or ReturnPath. Repeated hits inside a short window trigger an automatic lock, sometimes with a 522 error
  • A forwarder passing on spam that arrived at your address. The forwarded mail counts as yours

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If your site was compromised

A relay lock after a hack needs the cause removed before we can lift it, or it will simply recur:
  1. Complete a full malware clean-up — see Recovering a hacked site
  2. Remove any mailer scripts and backdoors, and rebuild core application files
  3. Rotate every credential — mailboxes, control panel, FTP, database
  4. Then ask us to remove the restriction
If there is already an abuse investigation ticket open about the account, reply on that ticket rather than opening a new one.

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IP reputation blocks

The errors: S3150, Senderscore, 550 5.7.1 citing Cloudmark Sender Intelligence, 554 Blocked citing Proofpoint, Barracuda, or 550 JunkMail RBL. These are different. Your account is not locked — one recipient’s provider is refusing mail from the shared outbound IP address because of its reputation. Mail to everyone else keeps working, which is the giveaway.

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What to do

Most of these providers run a self-service delisting portal, and a request from the sender is usually the fastest route: You will need the blocked IP address, which is in the bounce message. If you are not sure whether an IP belongs to our infrastructure, ask us and we will confirm it.
Some delisting forms send a verification email to the affected mailbox to prove you control it, so keep that mailbox accessible while the request is processed.
If lookup tools show the IP as clean but mail is still rejected, the recipient’s server may be using a cached or mirrored blocklist that lags behind the official one. That usually clears on its own.

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Check your own restrictions first

Before assuming a relay lock, check the mailbox has not simply had sending switched off:
  1. Log in to cPanel and open Email Accounts.
  2. Click Manage next to the address.
  3. Look at Restrictions and confirm outgoing mail and login are set to Allow.
  4. Click Update Email Settings.
If those are already set correctly, the mailbox has storage available, and your DNS records are right, then it is a server-level lock and needs us.

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Stopping it happening again

  • Authenticate your mail. Set up SPF, DKIM and DMARC. Unauthenticated mail is far more likely to be treated as spam, and on an unmanaged server sending direct it will often be refused outright
  • Move bulk and transactional mail off your hosting account. If an application sends in volume or in bursts, use a dedicated service — SendGrid, Mailgun or Amazon SES — which keeps it off the shared relay entirely. See Using external SMTP servers to send email
  • Respect the sending limits — 100 messages per hour, per domain
  • Do not forward spam. A forwarder that passes on junk is sending it as you