What should I put for my SPF record?
<p>I find the SPF Record Syntax at <a href="http://www.openspf.org/SPF_Record_Syntax" rel="nofollow">http://www.openspf.org/SPF_Record_Syntax</a> extremely cryptic and I don't understand it.</p>

<p>I have a number of PCs running jobs and which have to send out status emails. The domain of the sender email accounts for these notification emails is, say, <code>a.b.c.net</code>.  These PCs have private IP addresses on a LAN whose Internet connection is on DHCP, and hence their public IP address changes regularly.</p>

<p>These PCs are forward their mail to smtp.1and1.com to relay. Login credentials are required before smtp.1and1.com will relay.</p>

<p>What should the SPF record for a.b.c.net contain?</p>

<p>If I ping smtp.1and1.com, it is now 74.208.5.2, but I find that its value changes periodically. I inspected emails sent in this manner and the first relay is always:</p>

<pre><code>Received: from WINSHUS62 ([172.23.131.14]) by mrelay.perfora.net (mreueus002)
with ESMTPA (Nemesis) id 0M6URR-1Zth2s3kHT-00yRU8; Fri, 11 Mar 2016 15:55:41
</code></pre>