I used to read and respond to ingame mails using the web browser.
Since the forum change I am still able to do this. But I am unable to swap characters to one of my alts.
I only get an error.
How can I do this now?
And will there be a new web-based mail client available?
The current one tends to scramble the formatting of the mail.
you can try use API.
And before a Dev or ISD answers: Please refrain from recommending your android or ios apps, not everyone uses android or ios.
gate.eveonline.com is the site I normally use, but after the forum update, whenever I try to swap characters from within the same account I get this message:
Error
Sorry, an error has occurred while processing your request.
In other words they have broken the system with their new awesome forum login where you cannot switch chars without logging in and out either? Great work. Instead of improving the client with char selection without logging in and out, they expand the limitations of the game client to the forums and other services now. Absolutely fantastic.
But apart from EVE Gate and the official android app, I don’t think there are other ways to view and respond to mails.
At least you get mail 
This has been broken for a long time (and I’ve been told it’s been re-reported every patch since). If one or more of the characters on your account is docked in an Upwell structure this causes gate to bug out like you’ve seen.
I’m betting that when the CQ gets shanked (now tomorrow) the only safe place to log out will be space.
If you are looking for a web based solution, I wrote https://spacemail.tk
It’s more or less for personal/corp use and I do not advertise it a lot but its open to everyone.
Do you get that error on the SSO page?
No, the error occurs after you logged in and then try to switch characters via the menu bar at the top of the screen.
In the past, this used to be the case if one of your characters was docked at a citadel. I’m currently not and it works fine here.
When I am at this page: https://gate.eveonline.com/Mail/Inbox
I mouseover my portrait and name in the upper right corner, then I click “Select character” to switch character.
The following error occurs: “Sorry, an error has occurred while processing your request.”
This worked in july before my summer holiday.
Not a huge deal but I enjoyed checking and responding to ingame mail on multiple characters at this site.
Btw here’s a development idea: Make a new and updated mail system for web browsers 
Better idea is to community make such webpage based on API and CCP devs let focus on main game.
Probable won’t be big deal for any webmaster.
That is a most terrible idea. I do not want third parties to have even the remotest opportunities to write EVE mails because I gave their service read and write access so that I can respond to mails in a web browser. Community created things are also not reliable and futureproof, as the exodus of several PC programs in the recent past and mobile apps or the delayed fix to the Corp tag script for the forum (no hard feelings to the dev of that scrip, you just voluntarily fix screw ups of CCP) show.
Furthermore, the service already exists from CCP, which means there is no reason whatsoever this should get turned over into player hands.
Yep, you are right. But even if they want to upgrade/fix evegate. This will take some time since all hands are now on winter expansion and recent changes on login script (due change of board engine) force them to rewrite lot of that website/script.
I’ll take “Why developers drink for $1000, Alex”
Maybe, maybe if CCP exposed their in game mail API using the industry mail standards then maybe somebody could figure out how to configure some off the shelf webmail package to work with it. But they did not. As an added extra bonus CCP uses its own proprietary markup so good luck rendering that without heroic measures.
Even for a seasoned developer, implementing a web interface to EVE Mail requires a good amount of effort. Somebody who only knows HTML, CS and JavaScript is not going to succeed.
And yet there are still calls in the latest API (ESI) to both read and send mail. Super useful if you need to send automated mail (eg. welcome to corp, ops notification, etc.)
Judging by how broken some of gate’s features are putting one’s faith in CCP may be inadvisable. For extra giggles go poke through some of the SDE data and observe how they don’t seem to care if the same field is encoded as an int in one record and as a float in others.
I said “webmaster”. Knowing languages you mentioned is not even close to become one.
I made a website for this about a year ago. It still has some things I wanted to add to it. But you can reliably read your mails and do some pretty cool stuff, like deleting, advanced filtering, writing mails and more…
At the moment the site doesn’t store any information at all. So no need to be concerned about that. You will be communicating directly with the EVE server to get your mails.
On a final note. This service is currently online. I will extend the webhosting for another year. But I am not sure if I will keep it online longer than that, due to lack of (financial/ISK) support / interest of the EVE-community.
The site is: https://www.eve-mails.com/
A friend of mine once wanted to do what you do, but by having a client run, instead of an online service. They didn’t allow it, though, without any reason given. Might be, because he considered turning it into a program that eve players can use for sharing files, instant messaging, all the things. He even wrote a fake ftp client for this.
eventually he said, that the whole forums could be abused to save an infinite amount of data in a person’s posts, invisible for anyone but the poster himself. A madman, way ahead of his time.
Nice to see someone else eventually got permission. Are you using SSO and scraping gate.eveonline.com/mail/inbox, or is there a more modern way to do this?
There have been ESI endpoints for eve mails for a while now: https://esi.tech.ccp.is/latest/#/Mail
Edit: I just looked at the endpoints, they are quite nice