mail_alternatives_with_attachments | Send multipart alternative emails | Email library

So my current code is this in PHP:

I have an smtplib function that loops through 2 excel files and then opens them and adds them as an attachment. Right now the have generic names, but I thought it would be pretty cool to grab info from the data and use it as the name of the document. For example I wanted to grab their location based on a "Location" column found in a dataframe if Ive filtered by the user.

Goal: Rename 2 documents currently called "File1.xlsx" and "File2.xlsx" to "location_email_reminder1_3-4-2022" and "location_email_reminder2_3-4-2022"

Here's my code so far:

i am using sendgrid mail for sending email below is my code

Honestly, I think I have a fundamental gap in understanding how SMTP works. I can't seem to find a good explanation of what is happening behind the scenes and I think this is preventing me from being able to do what I am attempting to do.

To explain, I'm trying to setup an application which sends notifications to users by connecting to an SMTP server. Fair enough. I figure, since I'm using my own domain, I have SPF/DKIM/DMARC configured, I can add an MX record for the host I set the application up on (my SPF record has the mx keyword to authorize any hosts in my MX records to send/receive mails). Then, I can have that same host run a super lightweight SMTP server that can accept mails from the application, and send them on to recipients.

Almost crucially, I want this server to basically just run on localhost so that only this application can connect and send mails through it, but so that it can't really "receive" mails sent to my domain (I have set the MX priority very low (well, a high number) for this app server). I figure since I'm running my own SMTP server, that I don't really need to authenticate against it (it's running on localhost), just take in any mail and send it on to recipient domains.

When sending on to recipient domains... does the SMTP server need to authenticate to say, the gmail SMTP server as a user in order to send mails over there? That seems weird, since it's not a user logging into gmail to send mails, it's an SMTP server that is authorized within SPF sending mail from my domain (From address from my domain as well) to where ever the app server user's email is based (in this example, the user would be e.g., some_user@gmail.com).

I tried using python's aiosmtpd command-line and telnet to send a mail from test@MY_DOMAIN.TLD to test@MY_DOMAIN.TLD and it didn't seem to deliver the message; I figured aiosmtpd would connect to the preferred MX servers for my domain (my "real" MX's) to transfer the message, which would then put it in my inbox. That didn't seem to be the case, and I'm not sure why.

Exact repro steps, where example.com is my domain, and terminals are running on a box with a hostname listed in my MX records.

Terminal A:

Okay so I've a contact form I want people to select multiple items, once they submit the contact form I want it to send an email using a html template. I've set it up to string replace the data in the html template, but every time I try to do the array it ether says array or only shows one of the multiple items that were selected.

This is the HTML Select Code I made sure to add [] to make the name into an array.

I got an error once the form is submitted:
TypeError: e.preventDefault is not a function.

Here is my code:

I'm currently creating users using the next.js API, however, I now want to send emails using sendgrid.

I have this setup, however, I get the following

I am trying to send an email with CC & BCC. Emails are not delivered to CC & BCC addresses. But CC addresses are displayed to the recipient's details. A snapshot is given below.

I am using golang net/smtp with SendGrid. My code sample is given below.

I have been searching a lot for an answer, but I did not find my mistake yet. So maybe you can help me with this error I get when trying to send a mail from an unknown mail via nodemailer to my personal mail (for a contact form on my website):

api/mail.js