doveadm: Error: open(/proc/self/io) failed

[A. Schulze]

Am 31.07.19 um 08:27 schrieb Sami Ketola via dovecot:
> service lmtp {
>  user = vmail
> }
> 
> please remove user = vmail from here or change it to root.
> 
> for security reasons lmtp service must be started as root since version 2.2.36. lmtp will drop root privileges after initialisation but it needs to open /self/proc/io as root before that.

Hello Sami,

I don't read "root is required for lmtp" in https://wiki.dovecot.org/LMTP#Security neither does https://dovecot.org/doc/NEWS-2.2 say so.
Could you proof that statement somehow?

Andreas