Thank you for your reply Gordon,

I searched and read through both lists for any information about this issue first. Then I submitted this to the Vchkpw list, since this issue surely involves Vpopmail and I know how much the Courier list loves to answer Vpopmail questions. :O)

Yet, my testing makes me believe this is an issue with Courier-authlib and how it uses Vpopmail. More directly, in how Courier-authlib implements MySQL Replication that is configured in Vpopmail.

The reasons I believe this are ...

1) Vpopmail alone (used for SMTP Auth, and adding/deleting virtual domains) appears to correctly use the read DB for reads, and the write DB for writes. Only when using Courier-authlib for POP3 or Imap authentication does the problem show up.

2) Vpopmail does not use persistent DB connections natively, Courier-authlib implements these, and I'm seeing persistent connections appearing on the write/update DB (where I suspect there shouldn't be DB queries). i.e. I see connections to the write/update DB and also to the read only DB for a single POP3 authentication, which should only touch the read only DB.

I'm guessing that Courier-authlib is handing the DB access on it's own accord, and not simply calling vchkpw (or those persistent connections wouldn't be there). And I'm guessing it is within that DB handling that both DBs are getting accessed? Unfortunately, my C programming skills are between zero and none.