To troubleshoot this and get the data I needed, I just sent some test emails to my gmail account and found from the message header that all outbound traffic (for me) is coming from "mout.perfora.net" and put that in for my spf line shown below. You will need to verify the last hop server for yourself though.
ntxbg.org. 1800 IN TXT "v=spf1 include:mout.perfora.net ~all"
Here is the signature of what to look for in the header to get the name of the last 1and1 mail server before it hands off to the destination:
Received: from mout.perfora.net (mout.perfora.net. [220.127.116.11])
by mx.google.com with ESMTPS id e17si10739617wiw.45.2014.11.08.19.38.56
If you have your own DNS that can be updated with the SPF record either on another registrar or your own servers, 1and1 will work fine for email. Otherwise prepare to have much of your email marked as spam.