A great service. I've been doing something like this for > 20 years due to risk of breaches. I retire breached email accounts and make new ones to replace it, alas some email addresses are priceless as I joined gmail when it was in beta in 1997, and had a choice of easy nice names without numbers on them. So what I've done is made disposable email addresses that forward to my main email, and rarely give it out. Creating aliases on-the-fly that forward is a better alternative, so it preserves the main email, very much like how Virtual Account numbers use generated credit card numbers. The generated numbers are easily discarded and replaced. I also do this for my cellphone number, and change it periodically, since many providers allow this without cost, but keep an alias that is unchanged, but easy to change too if needed. Kudos to your team to think of new ways to enhance privacy and security.

The 150KB limit is a bit small, but adequate to inform the main email of a message from X. It would be helpful if during forwarding you stip photos, images etc., to save quota space, and transmit only text and attachments. Strip the attachment if it exceeds your limit. if you can provide a link to the native content if it exceed 150KB, and all such links expire in say X days , regardless to save server space and give users the opportunity to see the email at native size.