When comparing K-9 vs FastMail, the Slant community recommends K-9 for most people. In the question“What are the best e-mail clients for Android? ” K-9 is ranked 2nd while FastMail is ranked 18th.
Ranked in these QuestionsQuestion Ranking
Pro No privacy concerns
Pro Free an open source
K-9 is available for free and licensed under the Apache License version 2.0 with source code available here.
Pro Complete PGP encryption
It's possible to complete encrypt email communications via PGP using K-9.
K-9 mail does not use too many system resources when using the app, which allow it to be fast and lightweight.
Works well with locally maintained IMAP server.
Pro Material UI version
There is a fork of K-9 available on Google Play that uses Material design, improves the interface a lot.
Pro Excellent email threading
Threaded email support is better than most.
Pro Optimized for phone and tablet
On a tablet the UI looks a little different but given the extra real estate is logical.
Options to enable UI widgets a plus, can be enabled on a tablet and disabled on a phone.
Pro Traditional revenue model increases likelihood of personal data privacy and safety
Depending on your point of view, requiring to pay for Fastmail is actually a positive aspect of the service. This way you know the company is at least making some revenue (they have been around since 2010) and you know who the customer is. Pricing is as follows (go here for their on-site pricing info).
Pro Human support team
As you are their customer, Fastmail provides human support.
Pro Offers more control over email
Gmail has a tendency to dumb down the interface (try to sort by sender). Fastmail gives full control over email, just like a "traditional" client would.
Pro Custom sieve scripts
You can write your own Sieve scripts for filtering/rerouting email.
Pro Simple email actioning
Like gmail, you can "Pin" emails to the top of your inbox to deal with later with either a checkbox or the keyboard shortcut. Like Gmail you can also both archive and delete emails.
Supports two-factor authentication, one-time passwords and fully encrypted connections.
Pro Fully responsive interface
The Fastmail interface is fully responsive across all browser sizes.
Pro Offers IMAP migration tool
Get your old email out of Gmail easily with their migration tool.
Pro Adjustable spam filter
On writing this Fastmail has Basic, Normal, Aggressive or Customisable spam filtering which can be selected in the Advanced settings.
Each user has an individually trainable bayes database to improve spam filtering. You can train your personal bayes database by selecting some messages and using the Report spam and Report Non-Spam options from the Action menu on the Mailbox screen.
For IMAP users who don't use the web interface much, you can specify folders as spam/non-spam training folders on the Folders screen. Then just move messages into those folders as appropriate to train your bayes database.
For your personal bayes databases to be active, you have to train it with at least 200 spam messages and 200 non-spam messages. If you haven't trained enough messages, then we use a global continuously updated bayes database against your incoming messages, which helps detect spam/non-spam, but isn't as good as a personally trained one.
As Fastmail does away with all the extra bells and whistles of Gmail it is super fast to interact with. It also has faster IMAP and SMTP performance than Gmail.
Pro Integrated file storage
Fastmail allows saving attachments and other files into their own file storage system for easy retrieval later.
Pro Proper support for folders
FastMail has full support for folders, unlike Gmail where you only have labels.
Pro Intuitive default filters
Fastmail automatically filters your email into:
- Mailing Lists
Pro Identities & aliases practically gives you a new email that you can manage from a single account
With identities and aliases, you can set up a completely new email address that can be managed from your account, without paying for more. As of time of this writing, FastMail offers up to 500 identities and 600 aliases per account, regardless of plan type.
Con Noisy UI
The user interface is bland and tries to cram a lot of information on screen, making it unpleasant to use.
Con Emails received as forwarded EML attachments are not natively supported
When you receive an email which was forwarded as an EML attachment, K-9 Mail is not able to open it natively. It opens it using a third-party application registered for this mime-type on the device, if any. The Gmail email client app is able to read the EML attachments, thus you need to have it installed as well (or any other EML capable app).
Con Dead app
Con Australian law enforcement
The company and all email hosted by then is subject to Australian laws requiring sharing with law enforcement. These provisions are weaker than those provided by European GDPR.
Con Lacks folder notifications on official mobile app
The most popular domain registrars will provide you with both multiple email accounts and a domain name at a lower price than FastMail charges for only 1 email account.