Just new lessions leant after changing our SMTP smart host relay service provider (to MailJet.com). All e-mails, bounced by Pmail (external mails forwarded by our local users without editing) will be received by the SMTP relay but not forwarded. Instead of this they remain in a waiting queue, because of the sender addresses are not registered with the mail relay provider where only our domain is duly registered and authorized for sending mails.
Subsequently registering of each additional sender's address in these queued mails is generally possible but prctically not, since each of that addresses have to reply to a notification message from the SMTP relay to confirm the possession and legitimacy.
Is it possible to administratively block the bounce function in Pmail, that users could only forward mails with editing where the own sender's address will be added to the mail headers? I know that other mail clients even do not offer such a bounce function which is more and more complicated in times of spamming.