I have the same problem and the steps suggested on the standard BT Mail problems page do not assist - i.e.
* the emails are sent from regular correspondents who are simply "replying" to my emails;
* if the messages are simply "delayed", then they have been delayed for several days;
* I have checked my blocked addresses and none of the relevant correspondents has been blocked (whether inadvertently or otherwise);
* auto-forwarding has not been enabled;
* No "rules" have been set up.
Many of my e-mails seem to be getting through fine, but 3 or 4 correspondents have recently sent me significant messages (eg re appointments) which have not reached me.
Hi @Irefuteitthus and welcome to our community.
Do you know if the senders are getting any error messages? Your best bet would be to report this to Postmaster who should sort this for you.
Cheers
David