You can disable future incoming emails by using filters on the email account management of message options. Can't really see which device you are using in the mobile version of the forums. For example, on OS6, you hover on the email you want, press menukey then filters. Thereafter, choose on "when no filters apply:", and check "do not forward messages to the device".
If you only want to disable notifications, then use profile settings for that.
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For your first question, deleting an email address won't delete all your emails. They will be available in the messages app (the regular messages icon). If you re-add that address, all the emails will show up under it again (email icon). The email icon/shortcut on the device only acts similar to a filter for messages showing you the emails for that account only. While setting it up and having the service books let's you receive the emails for that account.
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