It sounds like potentially 2 different issues potentially at hand. Now I'm the one that provided the answer for the question regarding forwarding through Gmail and mine was done on an Ubuntu laptop configuration not CentOS and I unfortunately don't have a CentOS machine handy to test this on.

It sounds to me like the following may be causing the problems.

1. Check to ensure that the SASL binaries and libraries are installed. On my Ubuntu/Debian machines this would be including the libsasl2-2 and libsasl2-modules packages. The later actually provides the SO SASL modules while the former provides the SASL DB libraries.

2. Check to see if you have a trusted CA root chain certificate installed. On my Ubuntu/Debian machines I install the ca-certificate package which installs the known root level CA certificates and allows me to establish a CA cert chain that validates certificates signed by known CA's.

Updating to add after checking my Ubuntu laptop... The certificate issue is actually a non-critical issue so item #2 is likely not at fault as I get the same entries myself but mail is sent successfully which would lean more to item #1 being cause for failures to send.

Dec 12 07:51:56 solitare postfix/smtp[17525]: setting up TLS connection to smtp.gmail.com[74.125.67.109]:587 Dec 12 07:51:56 solitare postfix/smtp[17525]: certificate verification failed for smtp.gmail.com[74.125.67.109]:587: untrusted issuer /C=US/O=Equifax/OU=Equifax Secure Certificate Authority Dec 12 07:51:56 solitare postfix/smtp[17525]: Untrusted TLS connection established to smtp.gmail.com[74.125.67.109]:587: TLSv1 with cipher RC4-MD5 (128/128 bits) Dec 12 07:51:58 solitare postfix/smtp[17525]: 41C7212823B: to=<root@****>, orig_to=<root>, relay=smtp.gmail.com[74.125.67.109]:587, delay=2.4, delays=0.22/0.01/0.62/1.5, dsn=2.0.0, status=sent (250 2.0.0 OK 1292158318 b27sm3067589ana.28) 

It sounds like potentially 2 different issues potentially at hand. Now I'm the one that provided the answer for the question regarding forwarding through Gmail and mine was done on an Ubuntu laptop configuration not CentOS and I unfortunately don't have a CentOS machine handy to test this on.

It sounds to me like the following may be causing the problems.

1. Check to ensure that the SASL binaries and libraries are installed. On my Ubuntu/Debian machines this would be including the libsasl2-2 and libsasl2-modules packages. The later actually provides the SO SASL modules while the former provides the SASL DB libraries.

2. Check to see if you have a trusted CA root chain certificate installed. On my Ubuntu/Debian machines I install the ca-certificate package which installs the known root level CA certificates and allows me to establish a CA cert chain that validates certificates signed by known CA's.

Updating to add after checking my Ubuntu laptop... The certificate issue is actually a non-critical issue so item #2 is likely not at fault as I get the same entries myself but mail is sent successfully which would lean more to item #1 being cause for failures to send.

Dec 12 07:51:56 solitare postfix/smtp[17525]: setting up TLS connection to smtp.gmail.com[74.125.67.109]:587 Dec 12 07:51:56 solitare postfix/smtp[17525]: certificate verification failed for smtp.gmail.com[74.125.67.109]:587: untrusted issuer /C=US/O=Equifax/OU=Equifax Secure Certificate Authority Dec 12 07:51:56 solitare postfix/smtp[17525]: Untrusted TLS connection established to smtp.gmail.com[74.125.67.109]:587: TLSv1 with cipher RC4-MD5 (128/128 bits) Dec 12 07:51:58 solitare postfix/smtp[17525]: 41C7212823B: to=<root@****>, orig_to=<root>, relay=smtp.gmail.com[74.125.67.109]:587, delay=2.4, delays=0.22/0.01/0.62/1.5, dsn=2.0.0, status=sent (250 2.0.0 OK 1292158318 b27sm3067589ana.28) 

Fired up a CentOS 5.4 instance on Amazon EC2 and had a look around... In conjunction with item #1 on CentOS I would look to see if you have the following packages installed at a minimum: cyrus-sasl-lib, cyrus-sasl-plain and cyrus-sasl... There are other cyrus-sasl-* packages providing separate SASL modules if you should need them but the -lib and -plain should be the bare basics needed.