I created a (dv) account with Media Temple and my starting domain name becomes my name servers... Now they setup on there DNS server a reverse lookup for mydomain.com, but not for any of the domain names which go under it.
They won't setup a reverse lookup for any of your sub domains, unless they have a dedicated IP address, which costs $1.00 per month per IP address.
So what this means is say one of your sub-domains sends an email to myclient.com and it so happens that myclient.com like many other domains does a reverse lookup on incoming emails to verify its not spam, but since the reverse lookup doesn't exist, your sub domain gets an error message saying the email can't be delivered.
I emailed them and there first response was
It is not. All email originates from the main ip of the dv server, no matter how many IP addresses you have or do not have.
pointed me to http://www.openspf.org/Introduction and I was noticed this was also an option in Plesk, is it worth setting this up? Will my customers run into massive problems with email?
Are there any typical default settings for SPF that anyone knows off? Any feedback on this issue would be great! I am not entirely sure exactly what errors my customers will get... Will all emails they send to people bounce?
You can't predict how the existence or non-existence of a SPF record will affect delivery as that would be dependant on the recipients side.
Most likely the worst it would do is mail sent to popular hosted Webmail solutions (Hotmail, GMail, etc) would be more likely to flag the message as spam if it had no SPF record, or especially if it failed the SPF record check.
A typlical SPF record is:
example.com. IN TXT "v=spf1"
which really says nothing helpful.
You would add in "a", "mx", "ptr", and possibly "~all" or "?all"
example.com. IN TXT "v=spf1 a mx ptr ~all"
"a" means that any of the A records for example.com are authorized hosts to send mail for example.com.
"mx" means that any of the MX records for example.com are authorized hosts to send mail for example.com.
"ptr" means that anything with a reverse resolution within the domain example.com is authorized to send mail for example.com.
"~all" means that SPF queries that do not match any other mechanism will return 'softfail'. Messages that are not sent from an approved server should still be accepted but may be subjected to greater scrutiny.
"?all" means that SPF queries that do not match any other mechanism will return 'neutral'. Messages that are not sent from an approved server should still be accepted as if the SPF record did not exist.