Thank you for answer. But on old system is courier aprx 160 mail box - 150GB.
And I need to migrate it for 4 hours. Because need to start new system immediately after migration process.
If I will use courier on both systems - I only need to create the same users and to copy vmail folder it is all.
But if choose dovecot and migrate on it - it need much more time to migrate.
Need to copy each folder for each user.
May be you can to advise another steps for fast migration from courier to dovecot?