Right now, you have one pin each and store them in one place each.
If you want to use multiple pins (possibly for multiple purposes) a data structure such as an array would come in handy.
Arrays can hold multiple elements and allow you to easily access them sequentially.
Here’s an example, based on your code:

import RPi.GPIO as GPIO
import time
import smtplib

# Setup
GPIO.setmode(GPIO.BCM)
GPIO.setwarnings(False)

# Define your input and output GPIO pins
input_pins = [17, 27]  # Replace with your input GPIO numbers
output_pins = [2, 3]   # Replace with your output GPIO numbers

# Setup GPIO inputs and outputs
for pin in input_pins:
    GPIO.setup(pin, GPIO.IN, pull_up_down=GPIO.PUD_UP)

for pin in output_pins:
    GPIO.setup(pin, GPIO.OUT)
    GPIO.output(pin, GPIO.HIGH)

try:
    while True:
        # Loop through each input pin and check its state
        for i, input_pin in enumerate(input_pins):
            input_state = GPIO.input(input_pin)
            if input_state == False:
                print(f'Button {i + 1} Pressed')
                GPIO.output(output_pins[i], GPIO.LOW)
                print(f"RELAY {i + 1} FIRED")
                time.sleep(1.0)
                GPIO.output(output_pins[i], GPIO.HIGH)
                time.sleep(0.5)

                # Send an email
                smtp = smtplib.SMTP('server.com', port='587')
                smtp.ehlo()
                smtp.starttls()
                smtp.login('[email protected]', 'passwordhere')
                smtp.sendmail('[email protected]', ['[email protected]', '[email protected]'], f"Button {i + 1} Pressed - Content Of Email")
                smtp.quit()
                time.sleep(0.5)

except KeyboardInterrupt:
    # Clean up GPIO on CTRL+C exit
    GPIO.cleanup()
finally:
    # Clean up GPIO on normal exit
    GPIO.cleanup()

This example loops through the array of input pins and checks each one individually.
If you’d want to send emails to different recipients, a dict (different data structure) might be better suited.

Here is an example of watching multiple lines using gpiod (the Python bindings for libgpiod).

You are only interested in the input going low so for the line settings use edge_detection=Edge.FALLING rather than edge_detection=Edge.BOTH,
and for the pull-up add bias=Bias.PULL_UP.

You can include the output lines in the same request, or do them separately as per the toggle_line_value.py example.

So, say for lines 17 and 27, it could be something like:

import gpiod
from gpiod.line import Bias, Direction, Edge, Value

input_lines = (17, 27)
output_lines = (2, 3)
with gpiod.request_lines(
    "/dev/gpiochip0",
    config={
        input_lines: gpiod.LineSettings(bias=Bias.PULL_UP, edge_detection=Edge.FALLING), 
        output_lines: gpiod.LineSettings(direction=Direction.OUTPUT, output_value=Value.ACTIVE)},
    ) as request:
        while True:
            for event in request.read_edge_events():
              # do whatever based on the event
              if event.line_offset == 17:
                  # fire relay
                  request.set_value(2, Value.INACTIVE)
                  # ...

That is using the latest gpiod which you can install using:

pip install gpiod

And it doesn’t waste CPU cycles polling.