История изменений

Тогда, думаю, в этом и беда, что два довикота одновременно напрямую работают с одним хранилищем.
На docs.dovecot.org английским по белому:

Dovecot is commonly used with NFS. However, Dovecot does not support accessing the same user simultaneously by different servers. That will result in more or less severe mailbox corruption. Note that this applies to all mailbox access, including mail delivery.

• Use Dovecot director for clustering.
• Use LMTP Server for mail deliveries.

Тогда, думаю, в этом и беда, что два довикота одновременно напрямую работают с одним хранилищем.
На docs.dovecot.org английским по белому:

Dovecot is commonly used with NFS. However, Dovecot does not support accessing the same user simultaneously by different servers. That will result in more or less severe mailbox corruption. Note that this applies to all mailbox access, including mail delivery.

• Use Dovecot director for clustering.
• Use LMTP Server for mail deliveries.