SMTP Error (-1): Connection to server failed while sending emails from roundcube mail client

Feb  8 05:36:38 localhost postfix/anvil[15513]: statistics: max cache size 2 at Feb  8 05:33:17
Feb  8 05:37:00 localhost postfix/smtpd[15537]: connect from localhost[::1]
Feb  8 05:37:00 localhost postfix/smtpd[15537]: lost connection after UNKNOWN from localhost[::1]
Feb  8 05:37:00 localhost postfix/smtpd[15537]: disconnect from localhost[::1]
Feb  8 05:43:46 localhost postfix/smtpd[15553]: connect from localhost[::1]
Feb  8 05:43:46 localhost postfix/smtpd[15553]: lost connection after UNKNOWN from localhost[::1]
Feb  8 05:43:46 localhost postfix/smtpd[15553]: disconnect from localhost[::1]
Feb  8 05:56:11 localhost postfix/smtpd[15570]: connect from localhost[::1]
Feb  8 05:56:11 localhost postfix/smtpd[15570]: lost connection after UNKNOWN from localhost[::1]
Feb  8 05:56:11 localhost postfix/smtpd[15570]: disconnect from localhost[::1]

smtpd_relay_restrictions = permit_mynetworks permit_sasl_authenticated  reject_unauth_destination
myhostname = domain.com
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = localhost
relayhost =
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all