Is there a web-base version of eM?

I prefer not to be desktop based

No, eM Client is only desktop application.

I would be VERY happy to pay a monthly recurring fee for a web version of eM client. I have a destkop PC and a mac latoptop. Having a web version would mean everything was portable!

That would be a completely different product; most mailaccounts have their own webclient anyway and the point of eMClient is to have a desktop-app. So just use the existing webclient of your mailservice and if it does not have one or if you don’t like it, try a different one. You could even keep your address you are using now e.g. with Gmail. If you use eMClient with IMAP the “folder”-structure would be the same everywhere.

Actually in my opinion the combination of a good webservice and it’s features as a base with eMClient using IMAP as the “desktop-frontend” is the best setup. For example I setup filters on the web and have the webclient care for SPAM-control and eMClient only gets to work with the clean results. On the other hand eM has features like the mass sending that help circumvent shortcomings of the services webclients.

Of course it would be a completely different product - and a massive undertaking I’m sure. Something worth considering though. There is some logic to a cloud-based SAAS model, however. Recurring subscriptions and a larger customer base. I know with each new computer I get, I have less and less software locally installed. em client is now the only remaining desktop application I need to run my business. 

Yes, most mail accounts have their own web clients - but they are garbage. There are also free desktop email clients - also garbage. The point of em client is that it brings them all together in a powerful and reliable package. Why not have a web client that simply does it all - it does not yet exist. 

The market for desktop-E-Mail-apps is gravely limited as it is. And me personally, I prefer a “pay and own” model over the SAAS trend in almost any area. If I have a choice, I will always avoid a cloud based subscription model.