Here is what is happening.
I have domain example.com .
I have email@example.com forward e-mail to firstname.lastname@example.org .
email@example.com sends an e-mail to firstname.lastname@example.org .
The e-mail is forwarded to email@example.com .
In the header will be “softfail (google.com: domain of transitioning firstname.lastname@example.org does not designate 18.104.22.168 as permitted sender) client-ip=22.214.171.124;”
What is happening is when google gets the e-mail it checks the SPF record of the FROM address, the sender being example.org . It is checking if dreamhost’s IP address is permitted to send e-mail for example.org .
Many seem to use softfail, while others use fail (like PayPal.com), but they still go through eventually anyway.
I’m not sure what the delay is, but it seems to be exactly 3 hours for me, on somewhat random e-mails. Most e-mails I don’t notice the delay, so I’m not sure how often it happens. Maybe I’ll do a scan of 100 e-mails and see how many were delayed.