Just in case- I'll give you my email address just in case I'm not on Line
Highlights that they might need it and is a polite way to give it to someone.
You can add " I'm not on Line" to the end of the sentences to justify why you're giving the person your email address.
Just in case - I'll give you my email address just in case I'm not on Line（LINEで連絡が取れなかったときのためにメールアドレスを教えておきます）
「もしかすると必要かもしれないから」のニュアンスです。丁寧な言い方です。
文末に " I'm not on Line" を加えると、メールアドレスを教える理由がより明確になります。
この場合 念の為に で just in case がよく使われます。
教えておくは I'll tell you などでも良いですが口頭で伝えると
言った感じなのでSNSなどのやり取りの場合はあげておくで
I'll give you と言う表現を使う方が良いと思います。
「LINEが使えなくなったらここに連絡してね」
"Contact me here when you're unable to use LINE" など
Here's my email address in case you can't get me on LINE!
If I am not available on LINE, here's my email address!
"Here's my email address in case you can't get me on LINE!"
"If I am not available on LINE, here's my email address!"
"in case" meaning that if something happens you can be reached with a different method of communication.
The above examples mean that if you can't be reached via LINE then the person can contact you with your email address.
"Here's my email address in case you can't get me on LINE!"（LINEで連絡がつかなかったときのために、これ私のメールアドレスです）
"If I am not available on LINE, here's my email address!"
（LINEで連絡がつかなかったら、これ私のメールアドレスです）
"in case" は、何かがあったときには、他の手段で連絡ができることを表します。
上記の文は、もしLINEで連絡がつかないときには、メールアドレスで連絡ができることを表します。
If you can't get hold of me by text, I'll leave you with my email address
To someone you are texting on LINE and you want to tell them your email address, just in case, for some reason they can't contact with you by phone, then you may just use one of the above exampled sentences.
Here's my email just in case you can't reach me via LINE.
When we give someone our contact information, we often just use the word "here" to indicate that we are giving it to them. We use the verb "reach" to mean "contact." I hope that this helps. :)
The address you send emails to is call your 'email adress'
when you are telling someone something that they don't know but might need to use in the future you would say 'just in case'
Eメールアドレスのことは 'email adress' といいます。
将来必要になる可能性がある事を念のために伝えておくことは、'just in case' で表せます。
イギリス 
日本 
南アフリカ 
アメリカ合衆国 
