When a new Mailbos is created, the Mailbox doesn't contain a folder for the
sieve rules.

sieve = file:~/sieve/;active=~/.dovecot.sieve

As Long the directory ~/sieve does not exist, mails will be rejected.

Jul 15 14:42:59 wep001aa postfix/lmtp[8872]: E48E9358A1:
to=<support@example.com>, relay=mx.example.com[private/dovecot-lmtp],
delay=0.06, delays=0.01/0/0.04/0, dsn=4.2.0, status=deferred (host
mx.example.com[private/dovecot-lmtp] said: 451 4.2.0 <support@example.com>
Temporarily unable to access necessary Sieve scripts (in reply to end of DATA
command))


Jul 15 14:41:40 wep001aa dovecot[6754]:
lmtp(support@example.com)<8873><COX6OYR0LF2pIgAAiK8i3Q>: Error: sieve: file
storage: Performing t_readlink() on active sieve symlink '(null)' failed:
readlink() failed: Bad address
Jul 15 14:41:40 wep001aa dovecot[6754]:
lmtp(support@example.com)<8873><COX6OYR0LF2pIgAAiK8i3Q>: Error: sieve: Failed
to access active Sieve script in user storage `/var/vmail/example.com/support'
(temporary failure)
Jul 15 14:42:59 wep001aa dovecot[6754]:
lmtp(support@example.com)<8930><GdrqOtN0LF3iIgAAiK8i3Q>: Error: sieve: file
storage: Performing t_readlink() on active sieve symlink '(null)' failed:
readlink() failed: Bad address
Jul 15 14:42:59 wep001aa dovecot[6754]:
lmtp(support@example.com)<8930><GdrqOtN0LF3iIgAAiK8i3Q>: Error: sieve: Failed
to access active Sieve script in user storage `/var/vmail/example.com/support'
(temporary failure)



After this directory is created, mails will be delivered.

-> AFAIK ist shouldn't couse such a problem.