For those interested: you can change the default email font-size by copy/pasting the following css-code to Settings > Appearance > Custom Theme:

#conversation-view .message .frame {
font-size: 20px;
}

Hit the save-button and it should work! You can change the size to your wishes.

Geezer here: those of us over 40 generally are becoming progressively nearsighted, unfortunately.
Lots of "reader" eyeglasses being sold everywhere, proving the demographic need.
It would help...

I agree, having the option to increase the font size when reading e-mails (Small, Regular, Large) would be extremely appreciated. I read and write tiny font all the time but I find the tininess of the default ProtonMail font size when reading e-mails to be an eye-strain.

One key thing is adding inline images, properly. If I add an inline image I just took with my phone, it does an ENORMOUS (visually, and size-wise) attachment that can't be resized. So, I usually have to take a manual step by opening the pictures I want to include, in Photoshop, to make them smaller, before adding them to a protonmail message.

EMOTICONS!?!? WE DON"T NEED NO STINKIN' EMOTICONS!!! (Paraphrase - Treasure of the Sierra Madre 1948)

And I am SO completely kidding!

You are spot-on in fact. It is nearly 2018. Emoticons have been in use in emails since nearly the beginning. Now we have graphic emoticons, or more accurately, emoji, that have been standardized and incorporated into the Unicode consortium's Unicode Standard beginning with version 6 which included some 80 emoji and increased with each subsequent update of the standard to present with version 10 which now features more than 200 emoji!

I cannot speak to what, if any, risk the sender or receiver of an email containing an emoji might face, but I intuit that it is negligible, else their use would have fallen out of favor long ago.

So YES, DEFINITELY! Emoji ought to be made available to ProtonMail customers AS AN OPTION, just as plain text and HTML enhanced text are offered as options now.

And with that segue, let's briefly discuss the HTML text editor currently in use for customers that wish to use it.

I have just one thing to say: TinyMCE. Predominantly Open Source, very stable and almost an industry standard which some proprietary WYSIWYG text editor are jumping through hoops to compete with.

I am certain there is some rationale as to why TinyMCE was not implemented as the WYSIWYG text editor for ProtonMail from the beginning, but while some would find that interesting, it is really neither here nor there when discussing improving ProtonMail's text editing capabilities.

Yup, we really need a button to switch to "plain text only mode".

This is free secure service. Pick your battles, friends.

Planned..........since February 04,2016. That was 11/2 years ago .......

Definitely the Text Editor in the web interface needs some love :-)
It's almost the same since the first release of ProtonMail, but now it's time to improve it.

All of you must have perfect eyesight. I have low vision, and I would really REALLY appreciate if you could have an option of larger font or bold print. Even when I change the font size on my phone, it does not affect the font size on your app. Please please! Thank you. Otherwise really love your service.

The text editor for composing emails is VERY poor. It lacks many features that other email providers offer, such as: font type/family, font size, font color, text highlight, indent, inserting quotations, special characters, remove link, undo/redo and (god forbid!) some smilies/emoticons...

I see that this feature is planned. It would be helpful to know at least a rough timeframe for deploying this feature.

Is more than 2 years now and a simple font size feature is not available, Do You care?

I need a larger font size for email text. Many older people can not read small font sizes in email text. You have a very good email app and email system. Please allow a choice--add a larger email message text font. Thank you.

I need a choice of font size. Some folks receive email from me need larger font size. When I paste text into an email, I need to highlight it and adjust the font size. Please address these issues. Now that you've provided an expeditious way to import existing contact lists, protonmail will become my primary email service if I can adjust to its features & limitations. Thanks to all of you!

I would very much like to be able to change font size and style when composing a message. I use a lot of formatting when composing. Thanks.

This is definitely needed in the iOS app. I am in my mid 20s and I struggle to read the text in the app on my iPhone 5. It is hard enough to ask my parents to switch to another email service, and it will be practically impossible if they cannot read the text displayed on the phone's interface.

Us old farts Don t have eye like before
Bigger is good
Do it please !

The iOS app is unusable because the display font is so small. The light color makes it worse. You can't even zoom in on the inbox to see the sender and subject line.
I have to completely stop what I'm doing and concentrate on trying to decipher it
This is the only app I have problems with.
My only choices are to discontinue using Protonmail or use the iOS mail app.

...and color please.