I've been in a similar situation.
DP is a plumber, he came home one day and mentioned that the woman he was working for had offered him dinner and the use of her shower as he was working late (he declined).
I was surprised and teased him about how she obviously fancied him, who offers the plumber a shower?!! But he brushed it off, so oblivious..."no way, don't be silly" etc.
The next day, he went back. Knocked at the door but no answer. He had keys to the house (homeowner not always around) so let himself in. Although he THOUGHT no one was home, seeing as she didn't answer the door, he called out "anyone home" type thing when he opened the door. He continued to call out after having a quick check downstairs, and went up to the bathroom where he was working.
She FINALLY responded as he got upstairs and called him into her bedroom. She was sitting on the bed in her underwear
and chatted to him about the job. She WOULD have heard the door/him calling out. She wanted him to see her undressed, didn't flinch when he walked in, happily wafted around half naked while talking to him!
Knowing him, he wouldn't have known where to look and scooted off ASAP! He was mortified and admitted I was probably right!!!
Point being, some people are bloody brazen. Apparently this sort of thing happens every so often. All that matters is your DP's reaction. Has he replied to the email? Do you trust him?