here-document gives 'unexpected end of file' error

The EOF token must be at the beginning of the line, you can't indent it along with the block of code it goes with.

If you write <<-EOF you may indent it, but it must be indented with Tab characters, not spaces. So it still might not end up even with the block of code.

Also make sure you have no whitespace after the EOF token on the line.

The line that starts or ends the here-doc probably has some non-printable or whitespace characters (for example, carriage return) which means that the second "EOF" does not match the first, and doesn't end the here-doc like it should. This is a very common error, and difficult to detect with just a text editor. You can make non-printable characters visible for example with cat:

cat -A myfile.sh

Once you see the output from cat -A the solution will be obvious: remove the offending characters.

Please try to remove the preceeding spaces before EOF:-

/var/mail -s "$SUBJECT" "$EMAIL" <<-EOF

Using <tab> instead of <spaces> for ident AND using <<-EOF works fine.

The "-" removes the <tabs>, not <spaces>, but at least this works.