si.Mail Alternatives

si.Mail is described as 'Published under GPL (you don’t have to pay for it if you are using it, full source code availability)' and is a Email Client in the office & productivity category. There are seven alternatives to si.Mail for a variety of platforms, including Windows, Linux, BSD, Mac and PortableApps.com. The best alternative is Thunderbird, which is both free and Open Source. Other great apps like si.Mail are Microsoft Office Outlook, Claws Mail, Kontact - KMail and Sylpheed.

si.Mail alternatives are mainly Email Clients but may also be Calendar Apps or News Readers. Filter by these if you want a narrower list of alternatives or looking for a specific functionality of si.Mail.

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si.Mail

Free • Proprietary
Email Client
Windows

Published under GPL (you don’t have to pay for it if you are using it, full source code availability),

Learn more about si.Mail

Thunderbird
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Yes
No
Free • Open Source
Email Client
Calendar App
Mac
Windows
Linux
BSD
AppImageHub
Snapcraft
Flathub
PortableApps.com
Haiku
Homebrew
Chocolatey
93 alternatives to Thunderbird
Thunderbird is a free, open source, cross-platform e-mail, news and instant messaging client. The project strategy is modeled after Mozilla Firefox.
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Thunderbird Features
1. Extensible by Plugins/ExtensionsThunderbird can be extended with add-ons, plugins and extensions.
2. Multiple Account supportThunderbird support multiple accounts without the need to logout and login
3. Calendar IntegrationThunderbird lets you sync your tasks and events with your calendar application.
4. Email OrganizerThunderbird allows you to take control of your inbox by filtering and control tools.
5. Dark ModeThunderbird supports dark mode for comfortable usage in low light conditions.
6. Import/Export OPML FeedsImport and export your feed subscriptions into OPML format with Thunderbird.
7. PortableThunderbird can be used from a USB stick or similar with no prior installation.
8. Support for ThemesYou can use themes and templates to change the look and feel of Thunderbird.
9. Integrated Password ManagerThunderbird lets you access all the passwords you’ve saved across your different devices.
IMAP Support
SMTP Support
FOSS
Built-in RSS reader
POP3 Support
Add-ons
Intuitive
Graphical User Interface
Customizable
Built-in Calendar
Microsoft Office Outlook
Do you think this is a good alternative?
Yes
No
Paid • Proprietary
Email Client
Calendar App
Mac
Windows
Online
Android
iPhone
Android Tablet
Windows Phone
iPad
Apple Watch
Android Wear
135 alternatives to Microsoft Office Outlook
Microsoft Outlook, part of the Microsoft 365 (Office) (not to be confused with Microsoft Outlook Express), is a personal information manager that lets you manage your e-mail, calendar, contacts, and tasks.
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Microsoft Office Outlook Features
1. Email OrganizerMicrosoft Office Outlook allows you to take control of your inbox by filtering and control tools.
2. Calendar IntegrationMicrosoft Office Outlook lets you sync your tasks and events with your calendar application.
3. Calendar ViewMicrosoft Office Outlook has a built-in calendar view to have a clear overview of your content over time.
4. Support for AliasesMicrosoft Office Outlook supports aliases, so you can receive email without exposing your main email address
5. Unified inboxView e-mails (or similar) from all accounts in one unified view with Microsoft Office Outlook.
6. Multiple Account supportMicrosoft Office Outlook support multiple accounts without the need to logout and login
7. Works OfflineMicrosoft Office Outlook can be used without the need to connect to the internet.
8. Cloud SyncSync your data (notes, documents, bookmarks, etc.) across your different devices and to the cloud.
9. Dark ModeMicrosoft Office Outlook supports dark mode for comfortable usage in low light conditions.
Exchange
Native application
Onenote Desktop Integration
Contacts
Built-in Calendar
Address book integration
Onedrive integration
Smart attachments
Custom rules
Exchange Integration
Claws Mail
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Yes
No
Free • Open Source
Email Client
Calendar App
News Reader
Windows
Linux
BSD
88 alternatives to Claws Mail
Claws Mail is an email client (and news reader), based on GTK+, featuring

Quick response Graceful, and sophisticated interface Easy configuration, intuitive operation Abundant features Extensibility Robustness and stability.
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Claws Mail Features
1. LightweightClaws Mail consumes less device resources compared to similar apps.
2. Extensible by Plugins/ExtensionsClaws Mail can be extended with add-ons, plugins and extensions.
3. Multiple Account supportClaws Mail support multiple accounts without the need to logout and login
4. No registration requiredYou can use most of the features in Claws Mail without registration.
5. Import/Export OPML FeedsImport and export your feed subscriptions into OPML format with Claws Mail.
6. Spam FilterClaws Mail can detect unsolicited, unwanted and virus-infected emails, calls, files, etc.
7. PortableClaws Mail can be used from a USB stick or similar with no prior installation.
IMAP Support
Customizable
Multiple languages
Integrated Email Client
Content Filtering
Built-in RSS reader
Kontact - KMail
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Yes
No
Free • Open Source
Email Client
Linux
BSD
59 alternatives to Kontact - KMail
KMail is the email component of Kontact, the integrated personal information manager of KDE. Kontact is a personal information manager and groupware software suite for KDE. It supports calendars, contacts, notes, to-do lists, news, and email.
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Kontact - KMail Features
1. Email OrganizerKontact - KMail allows you to take control of your inbox by filtering and control tools.
Encryption methods
Sylpheed
Do you think this is a good alternative?
Yes
No
Free • Open Source
Email Client
Mac
Windows
Linux
BSD
PortableApps.com
48 alternatives to Sylpheed
Sylpheed is a simple, lightweight but featureful, and easy-to-use e-mail client (mailer, MUA).
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Sylpheed Features
1. LightweightSylpheed consumes less device resources compared to similar apps.
2. PortableSylpheed can be used from a USB stick or similar with no prior installation.
Gtk
POP3 Support
IMAP Support
The Bat
Do you think this is a good alternative?
Yes
No
Paid • Proprietary
Email Client
Windows
S/MIME
OpenPGP
60 alternatives to The Bat
The Bat! is a secure email client software, built to protect your correspondence against third-parties.
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The Bat Features
1. PGP EncryptionThe Bat supports PGP, an encryption system used for sending encrypted emails and files.
2. Support for scriptingThe Bat supports scripts and macros to automate or customize tasks.
3. GPG EncryptionThe Bat supports GPG (aka GnuPG) for encryption of things like emails, messages, files, etc.
4. PortableThe Bat can be used from a USB stick or similar with no prior installation.
Built-in RSS reader
POP3 Support
IMAP Support
S/MIME Support
SMTP Support
Pegasus Mail
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Yes
No
Free • Proprietary
Email Client
Windows
22 alternatives to Pegasus Mail
Pegasus Mail is a free, standards-based electronic mail client suitable for use by single or multiple users on single computers or on local area networks.
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Pegasus Mail Features
1. LightweightPegasus Mail consumes less device resources compared to similar apps.
Support for Multiple Users
IMAP Support
POP3 Support