Is somebody sending spam from my domain?
I'm using a custom domain and a catch-all alias that delivers all emails to this domain into my inbox. In the past few days, I started to get dozens of Mail Delivery Subsystem notifications that an email couldn't get delivered - originally sent from several user names on my domain that I never heard of. I'm suspecting somebody is trying to send spam from my domain and it occasionally fails to deliver, thus giving me this message.
I've set up my SPF record as recommended in the custom domain guide, as:
Should I perhaps make it more strict? The guide seems to recommend not doing so...