Adapting Bill Manville's technique, this should work for you. Go into **Data Validation** and select **Custom**. Enter this formula (assuming your email address is in cell A2):

```
=AND(ISERROR(FIND(" ",A2)),LEN(A2)-LEN(SUBSTITUTE(A2,"@",""))=1,IFERROR(SEARCH("@",A2)<SEARCH(".",A2,SEARCH("@",A2)),0),NOT(IFERROR(SEARCH("@",A2),0)=1),NOT(IFERROR(SEARCH(".",A2,SEARCH("@",A2))-SEARCH("@",A2),0)=1),LEFT(A2,1)<>".",RIGHT(A2,1)<>".")
```

Here's the same formula spaced out so it's readable:

```
=AND(
ISERROR(FIND(" ",A2))
,LEN(A2)-LEN(SUBSTITUTE(A2,"@",""))=1
,IFERROR(SEARCH("@",A2)<SEARCH(".",A2,SEARCH("@",A2)),0)
,NOT(IFERROR(SEARCH("@",A2),0)=1)
,NOT(IFERROR(SEARCH(".",A2,SEARCH("@",A2))-SEARCH("@",A2),0)=1)
,LEFT(A2,1)<>"."
,RIGHT(A2,1)<>"."
)
```

This checks that:

- There are no spaces
- Only one
`@`

symbol
- There are some characters before the
`@`

symbol
- At least one
`.`

symbol after the `@`

symbol
- At least one character between the
`@`

and following `.`

symbols
- The address doesn't start or end with
`.`