Now that the FREAK attack is widely disclosed, those of you who run SMTP servers that peer with clients that authenticate your server (be it via the traditional PKI or via DANE), might want to tighten-up your server cipher-suite settings just in-case:
smtpd_tls_exclude_ciphers = EXPORT, LOW
If nobody has yet elicited and factored any 512-bit RSA public keys from your server then your unpatched clients will be safe from the attack. (Not clear how you'd know this).
If your server might have already signed one or more export RSA keys then its clients are potentially exposed to the attack for the lifetime of the server's long-term RSA keys.
So, *after disabling* export grade algorithms, it may be prudent as appropriate to deploy new certificates. If you've published DANE TLSA records, follow the key rotation process described in:
https://tools.ietf.org/html/draft-ietf-dane-ops-07#section-8.1
Make sure to generate a new private/public key pair, rather than just re-use the existing key for a new certificate. Make sure to augment the TLSA record in DNS before deploying the new certificate, wait 2 TTLs or so, then deploy the new certificate and drop the obsolete instance of the TLSA record after.
Note that while Postfix clients that do mandatory TLS (authenticated or not) do not enable EXPORT ciphers, the reason the FREAK bug is important is that such clients accept ephemeral RSA key transport with a 512-bit key anyway, while ostensibly negotiating a cipher-suite that does regular RSA key transport. This is a failure to exclude state transitions that should be disallowed in the SSL/TLS protocol state-machine.