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. 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 will 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.