The built-in Android email application allows us to set a custom email signature which will be shown at the end of your email .
1. Open the Email inbox icon.
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2. In the Mail option, tap on Menu and then on the Settings button.
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3. Select your email account. If you have multiple accounts, you can set different signatures for each account.
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4. Tap on "Signature".
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5. Set your customized signature and then tap on the OK button.
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Now, whenever you send an email or reply to one, the signature will be automatically added at the end of your email.