Lorsque l'on utilise un SMTP de FAI grand publique pour relayer les mails (malheureusement, on a pas toujours le choix), il arrive que ce dernier refuse temporairement de les prendre en charge car nous envoyons soit disant trop de messages:

[root@sas ~]# tailf /var/log/qmail/current 
@400000004b161b702eaec47c delivery 186985: deferral: Connected_to_212.27.48.4_but_greeting_failed./Remote_host_said:_421_4.7.0_smtp1-g21.free.fr_Error:_too_many_connections_from_12.13.14.15/
@400000004b161b702eaedfd4 status: local 0/10 remote 4/20
@400000004b161b702eddfa6c delivery 186986: deferral: Connected_to_212.27.48.4_but_greeting_failed./Remote_host_said:_421_4.7.0_smtp1-g21.free.fr_Error:_too_many_connections_from_12.13.14.15/
@400000004b161b702ede505c status: local 0/10 remote 3/20
@400000004b161b702f384b84 delivery 186987: deferral: Connected_to_212.27.48.4_but_greeting_failed./Remote_host_said:_421_4.7.0_smtp1-g21.free.fr_Error:_too_many_connections_from_12.13.14.15/
@400000004b161b702f388234 status: local 0/10 remote 2/20
@400000004b161b702fa16d94 delivery 186989: deferral: Connected_to_212.27.48.4_but_greeting_failed./Remote_host_said:_421_4.7.0_smtp1-g21.free.fr_Error:_too_many_connections_from_12.13.14.15/
@400000004b161b702fa1a444 status: local 0/10 remote 1/20
@400000004b161b702fe12614 delivery 186988: deferral: Connected_to_212.27.48.4_but_greeting_failed./Remote_host_said:_421_4.7.0_smtp1-g21.free.fr_Error:_too_many_connections_from_12.13.14.15/
@400000004b161b702fe15cc4 status: local 0/10 remote 0/20

Pour éviter ça, il est possible de limiter le nombre de connexions sortantes concurrentes:

db configuration setprop qmail ConcurrencyRemote 5
signal-event email-update

Ça devrait permettre de limiter la casse

smtp mail