I'd like to enable the new Domain Keys DKIM email authentication feature for a domain hosted in Google Apps.

Some of my users use an external SMTP gateway (such that when they send email, it doesn't go through smtp.gmail.com).

I have an SPF record configured for the domain, and this allows the external SMTP gateways as valid SMTP hosts. (I realise SPF is different to DKIM)

Will enabling DKIM adversely affect the external gateway email? eg. Are the externally sent emails at risk of being marked as spam because they would not have the DKIM signature, or will DKIM only positively benefit emails sent through Google's SMTP server?


Your users can use an external SMTP server. But of course, their emails will have a worse reputation, compared to those directly sent from Google's server, and for two reasons :

  • The first one is that they won't be signed by DKIM (luckily the server is declared in the SPF record)
  • You'll send mails from a server that is not declared as a MX for the domain

We're just talking here about email reputation (ie the spam score). But don't worry it will work : You may just sometimes have mails seen as spam, in general with big companies with high spam protections (AOL, Yahoo, Gmail, Hotmail, ...).

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