Sendinblue is a third party sender based in France:

Aligned Authentication method:

SPF - No (there is a possibility this has been added recently but is as yet unproven)

DKIM - Yes TXT record

They support aligned authentication using DKIM. It is possible that they have added the ability to send in an SPF aligned way but this has not yet been confirmed.

Sendinblue has a verification process that checks to see if a customer has correctly published SPF and DKIM records before they will send in an aligned way. There are two issues that have bee identified with this to date:

SPF: Sendinblue does a simple text match for their SPF include and is not able to recognize the  Valimail Macros. They have the ability to bypass this behind the scenes

DKIM: Sendinblue's verification expects there to be no spaces between any of the components of the DKIM key. The DKIM standard supports whitespace so there is no requirement in the standard for this to be so. They are able to bypass this check behind the scenes

It is normally necessary to escalate within Sendinblue support since their front line support does not seem to be educated on this