A small Windows utility that accepts your mailto: links, asks which profile
you want to send from, and opens Gmail's compose window in your default
browser, in the right email account. No tray icon, no background service: it
starts, does one job, exits.
It supports any Gmail hosted email account, not just @gmail.
Teach it which profile to route your email to (ex: anything at this domain goes from my work account), and it will do it automatically! Without scripting, or hand-edited configuration files.
Click a mail link on Windows and it opens whatever Windows picked years ago, usually Outlook, whether or not you have ever used it.
Pointing it at Gmail instead is the obvious fix, and it works... until you have a second account. Gmail's own handler doesn't understand multiple gmail accounts: it just sends everything to the first mailbox signed into that browser profile, and composes there without asking. And as you sign in and out of email accounts, who knows what account it's going to pick to send from next time.
The message goes from the wrong address, and you find out after sending, if at all. This app puts the choice back in front of you: named mailboxes you pick, so the right account can send the right email.
Service wrapper clients like Ferdium are one common route to this. They host Gmail in a desktop window but cannot route a mail link to a particular account. It's a frustrating mess. But not anymore!
1. Download it. One file, GmailTo.exe, from the
latest release. It runs natively as 64-bit on 64-bit
Windows and as 32-bit on 32-bit Windows, so there is nothing to choose between.
2. Run it. Windows will say "Windows protected your PC", because the file is not code-signed. Click More info, then Run anyway. That prompt is expected — signing requires a certificate this project does not have.
Run from Downloads, your Desktop, or a temp folder and it copies itself to
%LocalAppData%\Programs\GmailTo\ on that first run, registers from there,
and hands over to that copy, so the app you go on using is the permanent one. No
admin rights needed. The file you downloaded is left where it is, yours to keep
or bin. If you would rather choose the location, put it somewhere first and it
leaves your choice alone.
3. Add a profile. It asks straight away. Give it a name and the Gmail address to send from.
4. Say yes to becoming the mail handler. It offers as soon as the profile exists. Two dialogs in a row on a first run is normal.
And that's it. Clicking a mailto: link anywhere now brings up the
picker.
Windows 10 or 11. Nothing to install.
It runs on .NET Framework 4.8, which ships with Windows 10 from the May 2019 update and with every Windows 11. If you are on an older Windows 10, it is a free download from Microsoft.
Clicking a mailto: link brings up the picker, unless a rule matches.
- Enter, or clicking the highlighted row, opens Gmail immediately.
- Clicking a different row selects it; click again, or press Enter, to send.
- Esc cancels and nothing happens.
The highlighted profile is whichever a rule names, or the first profile in the list. That list is reorderable, so the top entry is your default.
A rule maps a recipient to the profile that should write to them, either one exact address or a whole domain.
In the picker, not in an editor. Beside the profiles is a Remember box offering to always use the chosen profile for that address or for its domain. It defaults to remembering nothing and resets every launch, so a rule only exists because you asked for it.
Choosing again replaces an existing rule, which is also how you edit one: send to that recipient again, pick the right profile, remember again.
An exact address beats a domain rule covering the same recipient, so rules never need ordering.
Matching uses the first To address, or the first Cc/Bcc if there is no
To. A link can carry several recipients across different domains, so the
Remember box names its target — Always use for company.com — rather than saying
"this domain".
The picker does not appear. The message opens in the profile the rule names, and a notice in the corner says which profile and which rule. It never takes focus, and fades after a few seconds.
Nothing is sent. This opens a Gmail compose window, so a rule that fires wrongly leaves a draft in the wrong Gmail account, visible in the browser, with nothing delivered.
Hold Shift while clicking a mail link to force the picker anyway.
Click the notice, or just run the app, to see the last thing it did without asking: who it went to, which profile, which rule, and when. From there you can send the same message again from a different profile, or remove the rule.
Only the most recent is kept, and it clears once seen, superseded, or once you send anything manually. If you miss one, the rule that caused it is still listed.
Rules... in settings lists them with a Remove button. There is no add or edit there: the picker already does both.
Editing a profile's address repoints its rules. Deleting a profile deletes the rules aiming at it, and says how many first.
Run GmailTo.exe with no arguments. Profiles can be added, edited,
reordered and removed, and the button at the bottom toggles between Set as
default mail handler and Stop handling mail links depending on which state
you are in.
Stopping releases the association and removes the app's registry entries. Windows then falls through to whatever is next — as with any app that gives up an association, it cannot be handed back to whoever held it before.
%AppData%\GmailTo\config.json
{
"Profiles": [
{ "Name": "Personal", "EmailAddress": "you@gmail.com" },
{ "Name": "Work", "EmailAddress": "you@company.com" }
],
"Rules": [
{ "Kind": "Domain", "Match": "company.com", "EmailAddress": "you@company.com" },
{ "Kind": "Address", "Match": "friend@company.com", "EmailAddress": "you@gmail.com" }
]
}There is no Save button. Every change — profiles, rules, ordering — is written as it is made, and closing a window never discards anything. Removing a profile asks first and says which rules go with it.
Hand-editing is fine: Kind is written by name rather than as a number, and
rules point at profiles by address. An entry with no EmailAddress is dropped on
load. A corrupt file is reported, with an offer to reset it.
One other file lives beside it: last-forward.uri, holding the link of the last
automatic forward so it can be re-sent. It holds the draft, so it is deleted as
soon as it is used, seen, superseded, or a week old.
Run from Downloads, the Desktop, or a temp folder, it copies itself to
%LocalAppData%\Programs\GmailTo\ and registers from there. Those are the
places a file sits when nobody has decided where it belongs yet, and a handler
registered from one of them breaks the first time the folder is tidied.
Put the exe somewhere yourself and it stays put. A deliberate location is left alone, because silently relocating a file you filed on purpose is worse than the problem being solved.
Download the newer release and run it from Downloads. It replaces the installed copy, keeps the registration pointing at the same place, and leaves your profiles and rules alone. The download is left alone too, as ever.
To move an installed copy, move it and start it once in its new home. The registry entries name an absolute path, and the app repoints them at itself whenever the running copy is not the one on record — whichever copy you last started wins.
The repair happens on start, so you have to open the app yourself. A mail link cannot launch a path that is not there, and so cannot trigger it.
This does mean running a copy out of a build folder takes the registration too. When that happens the settings window says so and names the copy that has been orphaned.
All under HKEY_CURRENT_USER, no admin rights needed:
Software\Classes\mailto(+shell\open\command,DefaultIcon)Software\Classes\GmailTo.Url.Mailto— the ProgID that Capabilities and Windows' ownUserChoiceboth point atSoftware\GmailTo\Capabilities(+UrlAssociations\mailto)Software\RegisteredApplications→ valueGmailTo
Stop handling mail links removes all of them. Registering stashes whatever
Software\Classes\mailto held beforehand and stopping puts it back, so adding
and removing this app leaves an existing handler untouched.
There is no uninstaller, because there was no installer. Three steps, none of them needing admin rights:
- Open settings and click Stop handling mail links. That removes every
registry entry listed above and puts back whatever held
Software\Classes\mailtobeforehand. - Delete
%LocalAppData%\Programs\GmailTo\. - Delete
%AppData%\GmailTo\, which holdsconfig.jsonand any saved forward.
Step 1 cannot hand the association back to the app that held it before, because
Windows allows UserChoice to be deleted but never written. Mail links fall
through to whatever Windows decides is next, which is what happens to any file
association when the app owning it goes away.
Requires the .NET 8 SDK, which drives the build. It is not what the app runs on and is not needed to use it.
dotnet build GmailTo.csproj -c ReleaseOutput is bin\Release\net48\GmailTo.exe, and that one file is the whole
product. An AnyCPU binary runs natively as 64-bit on 64-bit Windows and as
32-bit on 32-bit Windows, so there is no second build, and with no package
references there is nothing to sit beside it.
The icon is ico\app.ico, six sizes from 16 to 256 pixels, each stored as a
32-bit PNG inside the .ico.
| File | Role |
|---|---|
Program.cs |
Entry point, argument handling, error dialogs |
MailtoRequest.cs |
RFC 2368 parsing and Gmail compose URL building |
EmailAddresses.cs |
Pulling a bare address out of a recipient field |
AppIcon.cs |
Loading the embedded icon for the windows |
Mail.cs |
Opening the Gmail compose window |
Config.cs |
config.json load/save, rules and matching |
RetryStore.cs |
The saved link of the last automatic forward |
PickerForm.cs |
The profile chooser, and where rules are created |
ToastForm.cs |
The corner notice, which must never take focus |
ForwardDialog.cs |
What happened, and how to undo it |
SettingsForm.cs |
Profile list editor |
ProfileDialog.cs |
Add/edit one profile |
RulesDialog.cs |
List and remove rules |
Registration.cs |
HKCU registry entries and self-healing |
SelfInstall.cs |
Copying itself to a permanent home on first run |
RegistrationPrompt.cs |
The offer to become the handler, and the walkthrough |
ConfigJson.cs |
Reading and writing config.json without System.Text.Json |
Compat.cs |
The few things .NET Framework does not provide |
app.manifest |
DPI awareness, compiled into the exe rather than beside it |
The forms are hand-written, with no .Designer.cs files, but follow the shape
the designer emits because WinForms depends on it — see
PLATFORM-NOTES.md before changing any layout code.
Two companion documents: DESIGN.md for why the app behaves as it does, and PLATFORM-NOTES.md for what had to be learned about Windows and Gmail to make it work.
MIT.
The origami bird icon in ico\ is original to this project and covered by the
same licence.