email validation

In addition to what Stefan suggested: i would strongly suggest you encapsulate such basic functionality as email address validation into a reusable Expression Rule, rather than hardcoding it onto any interface.

Is there a way, I can link the regex and expression rule and perform email validation.

regexmatch(
  pattern: "^[A-Z0-9\'\+\&\%_-]+(\.{0,1}[A-Z0-9\'\+\&\%_-]+)*[@]{1}[A-Z0-9.-]*[A-Z0-9-]+[.]{1}[A-Z]{2,6}$",
  searchString: ri!employee.email,
  regexFlags: "si"
)

You put that regex into an expression rule and call this in the validations parameter of your text field.

I don't have Regular Expression Plug-in, so not sure if I can use the pattern which I am talking.

Then install that plugin from the admin console.

You can also do a more simple check. E.g. just check for the existence of a @ and a dot. This would not require any plugin.

Not only @ , dot. I have to check at least few characters between @ and dot and few characters before @.

That would be a very simplified check.

a!forEach(
  items: {
    "this.is.my.email@example.com",
    "invalid.org",
    "missing.top.level@appian"
  },
  expression: like(
    fv!item,
    "*@*.*"
  )
)

That would be a very simplified check.

a!forEach(
  items: {
    "this.is.my.email@example.com",
    "invalid.org",
    "missing.top.level@appian"
  },
  expression: like(
    fv!item,
    "*@*.*"
  )
)

I have modified little bit, not it is working as per my requirement. Thank you so much for your help.

a!forEach(
    items: {
      "email@example.com",
      "invalid.org",
      "missing.top.level@appian",
      "swapna@.",
      "swapna@a.c"
    },
    expression: like(
      fv!item,
      "?*@?*.?*"
    )
  )

Like Mike I still strongly recommend using the regex or the people functions plugin.