After upgrading a server from Ubuntu 10.04 to 12.04, postfix is no longer sending email through sendgrid.com. I followed this guide about 6 months ago and everything had been working perfectly until the upgrade. Now it doesn't seem to be authenticating with sendgrid.

This is the error I get in my syslog when I try to send an email.

May 22 10:19:55 server postfix/smtp[3844]: 983B11C5DA: to=<to address>, 
relay=smtp.sendgrid.net[174.36.32.204]:587, delay=0.05, delays=0.01/0/0.04/0,
dsn=5.0.0, status=bounced (host smtp.sendgrid.net[174.36.32.204] said: 550 Cannot
receive from specified address <sendgrid username>: Unauthenticated senders not
allowed (in reply to MAIL FROM command))

This is from postconf -n

alias_database = hash:/etc/aliases
alias_maps = hash:/etc/aliases
append_dot_mydomain = no
biff = no
broken_sasl_auth_clients = no
config_directory = /etc/postfix
header_size_limit = 4096000
inet_interfaces = loopback-only
mailbox_size_limit = 0
mydestination = localhost, mylinode.members.linode.com
myhostname = hostname
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
readme_directory = no
recipient_delimiter = +
relayhost = [smtp.sendgrid.net]:587
smtp_sasl_auth_enable = yes
smtp_sasl_mechanism_filter = login
smtp_sasl_password_maps = hash:/etc/postfix/sasl/sendgrid
smtp_sasl_security_options = noanonymous
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
smtpd_banner = $myhostname ESMTP $mail_name (Ubuntu)
smtpd_tls_cert_file = /etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file = /etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
smtpd_use_tls = yes

Any help would be greatly appreciated. I would be happy to post any other logs or other relevant information.