Some Emails Remain On Remote POP account - SME Server

Situation
SME server is collectiing email from a remote POP account and fails to download particular emails but instead leaves them in the POP account marked as read.

Solution
Check the qpsmtpd settings by typing the following in the console.

config show qpsmtp

This will display your qpsmtp settings, which may vary from the following output.

qpsmtpd=service
    Bcc=enabled
    BccMode=bcc
    BccUser=maillog
    DNSBL=enabled
    LogLevel=6
    MaxScannerSize=25000000
    RBLList=bl.spamcop.net:combined.njabl.org:dnsbl.ahbl.org:dnsbl-1.uceprotect.                                             net:dnsbl-2.uceprotect.net:list.dsbl.org:multihop.dsbl.org:psbl.surriel.com:zen.                                             spamhaus.org
    RHSBL=enabled
    RequireResolvableFromHost=yes
    SBLList=bogusmx.rfc-ignorant.org:multi.surbl.org:black.uribl.com:bulk.rhs.ma                                             ilpolice.com:fraud.rhs.mailpolice.com:porn.rhs.mailpolice.com:adult.rhs.mailpoli                                             ce.com:ex.dnsbl.org
    TlsBeforeAuth=1
    access=public
    qplogsumm=disabled
    status=enabled

We are interested in RequireResolvableFromHost=yes

In the console type
config setprop qpsmtpd RequireResolvableFromHost no

Then to make the changes take effect
signal-event email-update

This should now allow the offending emails to be downloaded and removed from the remote POP account