Contact Form error mailbox given [] does not comply with RFC 2822, 3.6.2

So I need again your help guys. I'm building for the first time a contact form but despite my efforts, nothing.

The structure is the same, page "Contacts" with modular.md

<details>
<summary>modular.md</summary>

title: Contacts
cache_enable: false

form:
name: contact-form
action: /contacts
fields:

• name: form-name
  label: Name
  placeholder: Name
  autocomplete: on
  type: text
  validate:
  required: true

• name: form-email
  label: Email
  placeholder: Email
  type: email
  validate:
  rule: email
  required: true

• name: form-phone
  label: Phone
  placeholder: Phone
  type: tel

• name: textarea
  id: textarea
  label: messages
  placeholder: Tuo Messaggio
  type: textarea
  validate:
  required: true

  buttons:

• type: submit
  value: Send

  process:

• email:
  from: "{{ config.plugins.email.from }}"
  to:

  • "{{ config.plugins.email.from }}"
    subject: "[Contact] {{ form.value.name|e }}"
    body: "{% include 'forms/data.html.twig' %}"

• save:
  fileprefix: contact-
  dateformat: Ymd-His-u
  extension: txt
  body: "{% include 'forms/data.txt.twig' %}"

• display: thankyou

content:
items: '@self.modular'
order:
by: default
dir: asc
custom:

• _map

• _contact

</details>

Inside _contact sub-folder there is a form.md and form.html.twig has {% include 'forms/form.html.twig' %}

So the form is loaded perfectly but when I submit it, I got this error:
Address in mailbox given [] does not comply with RFC 2822, 3.6.2.

Email-Plugin is setted as SMTP with Mailtrap.io account, one personal email for "from" and "to", and I used different emails for submit test.
Everything is update.

I don't get what is going wrong, do you have any ideas?

Ok it seems I got the issue, on modular.md file there is

• name: form-phone
  label: Phone
  placeholder: Phone
  type: tel

I don't know if it needs some validation pattern in order to work propely, but by deleting it the form works fine.

What does the whole page frontmatter look like?

Sorry for the late reply @rhuk!
Actually there is not much more than what I wrote above but I try to be more detailed if you need.

I have a 06.contacts folder with a modular.md and 3 subfolders: _contact , _map , thankyou

lets skip the _map subfolder, these are the frontmatters:

<details>
<summary>modular.md</summary>

title: Contacts
cache_enable: false

content:
items: '@self.modular'
order:
by: default
dir: asc
custom:

• _map

• _contact

  form:
  name: contact-form
  action: /contacts
  fields:

  • name: form-name
    label: Name
    placeholder: Name
    autocomplete: on
    type: text
    validate:
    required: true

  • name: form-email
    label: Email
    placeholder: Email
    type: email
    validate:
    rule: email
    required: true

  • name: form-phone
    label: Phone
    placeholder: Phone
    type: tel

  • name: textarea
    id: textarea
    label: messages
    placeholder: Tuo Messaggio
    type: textarea
    validate:
    required: true

buttons:

• type: submit
  value: Send

process:

• email:
  from: "{{ config.plugins.email.from }}"
  to:
  • "{{ config.plugins.email.from }}"
    subject: "[Contact] {{ form.value.name|e }}"
    body: "{% include 'forms/data.html.twig' %}"
• save:
  fileprefix: contact-
  dateformat: Ymd-His-u
  extension: txt
  body: "{% include 'forms/data.txt.twig' %}"
• display: thankyou

</details>

<details>
<summary>form.md in _contact subfolder</summary>

title: Form

</details>

<details>
<summary>formdata.md in thankyou subfolder</summary>

title: Thankyou !

Your email has been sent!

</details>

As I said the problem was I setted a field type in the form as "tel" , by deleting it or changing it to "text" it worked fine.

Hope this may help and thanks for your great work on Grav!

I'm getting this same error.
I set up a form a week or so ago with no issue. I'm revisiting it make changes to the fields. Whenever I make a change and test the form, I get this error.

<details>
<summary>YAML</summary>

---
title: New Art
access:
  site.login: true
  admin.login: true
visible: false
form:
    name: contact-form
    fields:
        - name: customer
          label: Customer
          placeholder: Enter customer name
          autofocus: on
          autocomplete: on
          type: text
          validate:
            required: true

        - name: contact
          label: Contact
          placeholder: Enter contact name
          type: text
          validate:
            required: true

        - name: phone
          label: Contact Phone Number
          placeholder: Enter contact phone number
          type: text
          validate:
            required: true

        - name: email
          label: Email
          placeholder: Enter contact email address
          type: email
          validate:
            required: true

        - name: datein
          label: Date In
          placeholder: Enter date new job is created
          type: date
          validate:
            required: true

        - name: designdue
          label: Design Due Date
          placeholder: Enter due date for design
          type: date
          validate:
            required: true

        - name: inhands
          label: In Hands
          placeholder: Enter date customer wants product in hands
          type: date
          validate:
            required: true            

        - name: product
          label: Product
          placeholder: Enter product name and number (A link to product blank is best)
          type: text
          validate:
            required: true

        - name: description
          label: Description
          placeholder: Enter any additional helpful information
          type: textarea
          validate:
            required: true

    buttons:
        - type: submit
          value: Submit
        - type: reset
          value: Reset

    process:
        - email:
            from: "{{ config.plugins.email.from }}"
            to:
              - "{{ config.plugins.email.to }}"
              - "{{ form.value.email }}"
            subject: "[Feedback] {{ form.value.name|e }}"
            body: "{% include 'forms/data.html.twig' %}"
        - save:
            fileprefix: feedback-
            dateformat: Ymd-His-u
            extension: txt
            body: "{% include 'forms/data.txt.twig' %}"
        - message: Thank you for your feedback!
        - display: thankyou
---

</details>

The form works as it is above. Small changes will throw an error though. For instance:

• If I change validate.required to false on email, I get the error. I can change validate.required to false on the other fields with no problem.
• If I change type to text instead of email, I get the error.
• If I remove any of the list items under fields, I get the error.
• I can delete all fields except for email and it works. If I change the name of the field from email to something else, it then gives that error again. Have I somehow broken something by giving the field name: email ?

It makes no sense to me why these small changes would create this error. Any insight would be appreciated!