Improved documentation

docs/installation/email.md

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+---
+title: Email
+layout: default
+parent: Installation
+nav_order: 12
+---
+
+# Email
+
+Part-DB can communicate with its users via email. 
+At the moment this is only used to send password reset links, but in future this will be used for other things too.
+
+To make emails work you have to properly configure a mail provider in Part-DB.
+
+## Configuration
+Part-DB uses [Symfony Mailer](https://symfony.com/doc/current/mailer.html) to send emails, which supports multiple
+automatic mail providers (like MailChimp or SendGrid). If you want to use one of these providers, check the Symfony Mailer documentation for more information.
+
+We will only cover the configuration of a SMTP provider here, which is sufficient for most usecases.
+You will need an email account, which you can use send emails from via password-bases SMTP authentication, this account 
+should be dedicated to Part-DB.
+
+To configure the SMTP provider, you have to set the following environment variables:
+
+`MAILER_DSN`: You have to provide the SMTP server address and the credentials for the email account here. The format is the following:
+`smtp://<username>:<password>@<smtp-server-address>:<port>`. In most cases the username is the email address of the account, and the port is 587.
+So the resulting DSN could look like this: `smtp://j.doe@mail.invalid:SUPER_SECRET_PA$$WORD@smtp.mail.invalid:587`.
+
+`EMAIL_SENDER_EMAIL`: This is the email address which will be used as sender address for all emails sent by Part-DB.
+This should be the same email address as the one used in the `MAILER_DSN` (the email adress of your email account):
+e.g. `j.doe@mail.invalid`.
+
+`EMAIL_SENDER_NAME`: This is the name which will be used as sender name for all emails sent by Part-DB. 
+This can be anything you want, e.g. `My Part-DB Mailer`.
+
+
+Now you can enable the possibility to reset password by setting the `ALLOW_EMAIL_PW_RESET` env to `1` (or `true`).