I currently have postfix set up to relay messages from my websites through gmail, and up until recently it was working perfectly. However, within the last week or so (not really sure when) I started getting the below error whenever attempting to send an email:

Jul 20 07:40:46 localhost postfix/smtp[11958]: connect to smtp.gmail.com[2001:4860:800a::6c]:587: Network is unreachable
Jul 20 07:40:46 localhost postfix/smtp[11958]: connect to smtp.gmail.com[173.194.76.109]:587: Connection refused
Jul 20 07:40:46 localhost postfix/smtp[11958]: connect to smtp.gmail.com[173.194.76.108]:587: Connection refused

Here is my configuration file:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version

# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

#readme_directory = no

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.

myhostname = [my domain name]
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
#myorigin = /etc/mailname
mydestination = [my host name], localhost.localdomain, localhost
relayhost = [smtp.gmail.com]:587
mynetworks = 127.0.0.0/8
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = loopback-only
inet_protocols = all

##########################################
##### non debconf entries start here #####

##### client TLS parameters #####
smtp_tls_loglevel=1
smtp_tls_security_level=encrypt
smtp_sasl_auth_enable=yes
smtp_sasl_password_maps=hash:/etc/postfix/sasl/passwd
smtp_sasl_security_options = noanonymous

##### map username@localhost to [email protected] #####
smtp_generic_maps=hash:/etc/postfix/generic

Nothing changed on my server, as far as I know...any ideas what could have caused it to stop working?