I have already use the login aspect, but besides I want that one mail work over 1 device only. Actually I have very private site and want security as much as I can.
(Question Changed!!)
IMEI, MEID, ESN or IMSI Can use these aspects. If I can,
How to-
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Get them
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Check
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Block
I found this article Helpful - https://medium.com/@ssaurel/how-to-retrieve-an-unique-id-to-identify-android-devices-6f99fd5369eb
See if you too.