I noticed, and I think this feature is cool as hell. (and hell is pretty cool)
Quoted from robin:I have also been quietly rolling out another pretty cool feature: direct replying to PM notifications!
You may have already spotted the ---reply above this line--- text in PM notifications. Yes, you can indeed hit reply now in your e-mail client and your reply e-mail will be sent to the PinsideMail system which will automatically add it in the PM thread. Note how the To: line says "[name] via PinsideMail".
Super handy for quickly replying to PMs on, for example, your mobile phone!
Note: no support for attachments yet and only content above the ---reply--- line will be accepted/added.
Note2: Still in *beta*, use at your own risk. Make sure to check if your replys are showing up in PM threads. If something works weird, please contact me with details about your mail client etc.