Max. Number of char in a TXT Record

[Michael Milligan]

Darvin Denmian wrote:
> Hello,
> 
> I have some questions:
> 
> 1) Anybody know the maximum number of characters allowed in a TXT field?

255 for each string.  E.g.,

@      TXT  "v=spf1 mx ip4:216.208.1.1 a:mail01.mydomain.com
a:mail02.mydomain.com"  " a:mail03.mydomain.com
include:something.else.com -all"

Notice there are two sets of quoted text here to simulate the entire TXT
string being longer than 255 chars.  You'd just split it up into
multiple quoted strings that each are not longer than 255 chars.

Note that there is a leading space in the second string.  For SPF
processing, these TXT strings are concatenated together as-is and
without the leading space in the second string, it would generate a
syntax error.

> 
> 2) What is the maximum number of includes inside a SFP field?
> 

Don't chain them more than 2 or 3 times, you'll run into SPF processing
limits.  If you have to use more than that, then you need to rethink
you're matching approach.

The RFCs on the subject limit DNS lookups to 10, that includes the TXT
record itself, any A, MX and PTR records that have to be looked up by
name, and any further "include:" lookups and associated records.  A
Permanent Error will be returned if you exceed the 10 lookup limit.

See http://www.openspf.org/, there are tools, tips and tricks to help you.

Regards,
Mike

-- 
Michael Milligan                                   -> milli at acmeps.com