I get DMARC reports sent from various different sources. All of the reports generally have <result>pass</result> for all of the sections.

However, the reports from Google always have SPF fails:

<row>
    <source_ip>185.116.215.174</source_ip>
    <count>1</count>
    <policy_evaluated>
        <disposition>none</disposition>
        <dkim>pass</dkim>
        <spf>fail</spf>
    </policy_evaluated>
</row>
.
.
.
<auth_results> 
    <dkim>
        <domain>domain.co.uk</domain>
        <result>pass</result>
        <selector>dkim</selector>
    </dkim>
    <dkim>
        <domain>email-od.com</domain>
        <result>pass</result>
        <selector>dkim</selector>
    </dkim>
    <spf>
        <domain>bounce.domain.co.uk</domain>
        <result>fail</result>
    </spf>
</auth_results>

My SPF record looks like:

"v=spf1 +a +mx +a:server.domain.co.uk include:email-od.com ~all"

I am unsure why my bounce domain is failing SPF checks, but it only seems to be on Google DMARC reports.

To be honest, I am unsure what the bounce domain bounce.domain.co.uk does, should I set up an email address [email protected]?

Any help sorting my SPF and advice regarding bounce.domain.co.uk would be great.