Email delivery mainly depends on your recipient's email service. However, to maximize your odds of success, there are a few things you need to do:
- Publish an SPF (Sender Policy Framework) policy on your domain
Your SPF policy must be published via a TXT record. If you use Gandi's SMTP service exclusively to send your messages, this TXT record must be :
@ 10800 IN TXT "v=spf1 include:_mailcust.gandi.net ~all"
This SPF policy authorizes only Gandi's mail servers to send messages for your domain. If you publish this SPF policy, you must therefore make sure that you only send your messages via our SMTP service (mail.gandi.net or our webmails).
Should you need to use another SMTP service, such as that of a specialized SMTP provider, you must ask this provider to give you the address(es) of the SMTP server(s) to be authorized in the SPF policy published for your domain. Your provider will often send you a complete SPF policy such as "v=spf1 include:spf.example.com -all". You'll need to merge this policy with the one already published on your domain, which will yield, to use the example above:
@ 10800 IN TXT "v=spf1 include:_mailcust.gandi.net include:spf.example.com ~all"
It's important not to publish two different SPF policies on your domain.
Publish an SPF policy on your domain name
- Enable DKIM signature on your outgoing emails
The DKIM signature on your messages can help recipient servers authenticate them.
Enable the DKIM signature of your emails
- More generally, the content of your messages also influences the way they are processed by the receiving servers. For example, the inclusion of certain words (relating to drugs supposed to improve erectile dysfunction, or miraculous financial gains, for example) is not well regarded by the servers that receive your messages. But the same applies to a multitude of little factors relating to the way in which your messages are written (for example, sending an email with a subject in ALL CAPS sends a very bad sign to your recipients' anti-spam filters; another example: including a link to a malicious website can cause your email to be filtered out).