Someone types tom.f@gmal.com into your signup form. The address has the right shape, so a syntax check passes it. A suggestion would be more useful than telling them the format is fine.
The didyoumean field on /email gives you that suggestion when the domain is a known typo. This response is shortened to the relevant fields:
GET /email/tom.f@gmal.com
{
"email": "tom.f@gmal.com",
"didyoumean": "tom.f@gmail.com",
"valid": true,
"domain": "gmal.com"
}
The email field contains the input after the usual trimming and lowercasing. didyoumean contains the complete suggested address, so a form can show it as a choice without assembling another string. It is part of the basic response and does not need ?deep=true.
The typo correction only changes the domain. If the input is tmo.f@gmal.com, the suggestion is tmo.f@gmail.com. The API has a known correction for gmal.com, but it has no basis for changing tmo.f to tom.f.
When there is no known correction, the field is null. When there is a suggestion, show a choice such as "Use tom.f@gmail.com?" and let the person confirm it. Keep their original address if they decline.
If they accept, check the corrected address before using it. The first response's domain and mailbox findings belong to gmal.com, not to the suggested Gmail address. A typo suggestion doesn't transfer a validation result from one inbox to another.