Read the queue before you flush it.
Exim or Postfix, thousands of frozen or deferred messages. A flush of spam is how the IP gets listed. The cause is a sender, a disk, or a remote reject.
One mailbox, a script, or the world saying no
A compromised mailbox or a web script under that user. We stop submission for that account, rotate the password, and leave the other domains sending.
A 550, greylisting, or a missing PTR. Flushing retries the same reject. The log line is the fix, not the queue length.
The spool filled the volume. Mail cannot be delivered or received. Space first, then the queue. Deleting the spool directory is not the repair.
Hestia and DirectAdmin are Exim. A hand-built VPS is often Postfix.
The commands differ. The decision does not: identify the sender, stop the source, remove only the spam, retry the legitimate mail. A panel button that says “delete queue” is how a customer invoice disappears.
€55 an hour. Mail stopped for everyone is emergency, if someone is free.
Minimum 1 hour. Emergency €95, subject to availability. A delist, if the IP is already listed, is a separate and slower problem.
Queue in the thousands?
Tell us Exim or Postfix, and whether one domain is the sender. No mailbox password in the first message.