Ошибка буфера памяти почтового сервера

Время от времени мой почтовый сервер перестает отправлять новые письма. Когда это произошло, я нахожу журнал ошибок ниже:

Jun 22 23:10:18 myserver saslauthd[3967]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:18 myserver saslauthd[3971]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:19 myserver saslauthd[3972]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:19 myserver saslauthd[3968]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:20 myserver saslauthd[3969]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:20 myserver saslauthd[3967]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:21 myserver saslauthd[3971]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:21 myserver saslauthd[3972]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error
Jun 22 23:10:22 myserver saslauthd[3971]: DEBUG: auth_pam: pam_authenticate failed: Memory buffer error

Каждый раз, когда мне приходится перезапускать сервер, чтобы снова нормально работать.

Я также всегда нахожу приведенный ниже журнал повторяющихся ошибок с неизвестного IP-адреса (я не уверен, связано это или нет):

Jun 21 06:48:43 myserver sshd[1687]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=************  user=root
Jun 21 06:48:45 myserver sshd[1708]: Failed password for root from ######## port 60021 ssh2
Jun 21 06:48:47 myserver sshd[1708]: Failed password for root from ######## port 60021 ssh2
Jun 21 06:48:47 myserver sshd[1708]: Received disconnect from #######: 11:  [preauth]
Jun 21 06:48:47 myserver sshd[1708]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=************  user=root
Jun 21 06:48:47 myserver sshd[1730]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=************  user=root
Jun 21 06:48:48 myserver sshd[1732]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=============  user=root
Jun 21 06:48:48 myserver sshd[1730]: Failed password for root from ************ port 60094 ssh2
Jun 21 06:48:50 myserver sshd[1732]: Failed password for root from ============ port 40613 ssh2
Jun 21 06:48:50 myserver sshd[1730]: Failed password for root from ************ port 60094 ssh2
Jun 21 06:48:50 myserver sshd[1734]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=************  user=root
Jun 21 06:48:52 myserver sshd[1736]: pam_unix(sshd:auth): authentication failure; logname= uid=0 euid=0 tty=ssh ruser= rhost=************  user=root
Jun 21 06:48:52 myserver sshd[1732]: Failed password for root from ============ port 40613 ssh2
Jun 21 06:48:52 myserver sshd[1730]: Failed password for root from ************ port 60094 ssh2
Jun 21 06:48:52 myserver sshd[1730]: Received disconnect from ***********: 11:  [preauth]
Jun 21 06:48:52 myserver sshd[1730]: PAM 2 more authentication failures; logname= uid=0 euid=0 tty=ssh ruser= rhost=***********  user=root
Jun 21 06:48:52 myserver sshd[1734]: Failed password for root from ######## port 47803 ssh2
Jun 21 06:48:54 myserver sshd[1736]: Failed password for root from ######## port 55371 ssh2
Jun 21 06:48:54 myserver sshd[1732]: Failed password for root from ============ port 40613 ssh2