550 firstname.lastname@example.org Invalid SPF record. Please inspect your SPF settings, and try again. IB508
The sending email address's domain has an SPF record that does not authorize the sending email server to send email from the domain.
Modify the SPF record to include the server you are trying to send from, or remove the SPF record from the domain.
You may want to communicate with them and ask them to send you from a different address (like a gmail account), and also tell them that they have a misconfiguration in their SPF record. Maybe you get a free coffee 😉
Hope it helps!
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