I am adding a domain (xero.com) to our existing SPF record, to allow marketing emails to be sent from an external system and appear as if they are from us.
The SPF record for xero.com is large and including it would take our own SPF record over the 10 lookup limit, resulting in error
Permanent Error: Too many DNS lookup
This is unfortunate, but what effect if any does this error actually have (for both hard and soft fail)?
Will it prevent any mail being sent, or allow all, or just ignore this included domain?
In addition to this, we advise some of our clients to include our domain in their SPF records so we can send mail on their behalf.
Could increasing the included domains on our SPF record have a negative impact on theirs?
Conversely, if I get round this problem by setting our SPF record to
v=spf1 +all to allow everything, could this also have an undesired effect for our clients that might use our domain in their SPF record?