For standards like SPF and DKIM / DomainKeys, whether they improve deliverability or bypass filters is entirely at the discretion of the validating receivers. It is expected that messages from a sender with a good reputation would be subject to less scrutiny by the receiver’s filters. [1] In other words, omitting these standards usually doesn’t hurt, but providing them can only help deliverability.

Some other things to consider:

  • DKIM is an internet standards track standard and deprecates DomainKeys
  • If you turn off DomainKeys we’ll still sign the email with DKIM which is not affected by the on behalf of issue, and is designed for the type of third-party signing we do.
  • An SPF record is invalid if it requires more than 10 DNS lookups
  • An SPF record is invalid if you have more than one SPF record for a given domain. In this case you will want to merge the additional SPF records into one SPF record.

[1] DKIM Frequently Asked Questions