Hyphen-separated email domain names are registered as invalid if they lack consecutive alphabetical characters

[frymash]

In the usage guide for the email field, it is stated that:

The domain name must:
    - end with a domain label at least 2 characters long
    - have each domain label start and end with alphanumeric characters
    - have each domain label consist of alphanumeric characters, separated only by hyphens, if any.

However, hyphen-separated email domain names (which follow the specification above) occasionally do not work. It seems like this issue happens when domain labels contain no consecutive alphabetical letters.

For instance, these emails are considered invalid by the app:

1. example@a-a-r-o-n
2. example@a-a-r-o-n-n-n-n-n-n

These emails, on the other hand, are still considered valid (as expected):

1. example@a-a-r-o-nn-n-nn-n
2. example@a-a-r-o-nn-n-nnn

Screenshot of issue

[nus-pe-script]

Your response not required for this bug as the team has accepted the bug as it is.