Python - Send email

import smtplib
from os.path import basename
from email.mime.application import MIMEApplication
from email.mime.multipart import MIMEMultipart
from email.mime.text import MIMEText


def send_mail(mail_server, send_from, send_to_list, subject, text, text_color='black', files=None, username=None, password=None):
 assert send_to_list
 assert isinstance(send_to_list, list)

 msg = MIMEMultipart('related')
 msg['From'] = send_from
 msg['To'] = ','.join(send_to_list)
 msg['Subject'] = subject
 warnings = []
 attachments = []

 if files and isinstance(files, list):
 for file in files:
 try:
 with open(file, 'rb') as f:
 attachment = MIMEApplication(f.read())
 # After the file is closed
 attachment['Content-Disposition'] = 'attachment; filename={}'.format(basename(file))
 attachments.append(attachment)
 except FileNotFoundError:
 warnings.append('WARNING: Attachment {} was not found!'.format(basename(file)))

 body_template = '<pre><font color={}>{}</font></pre>'
 if warnings:
 body_template = '<pre><font color={}>{}</font></pre>' + '<br><br>' + '<pre>{}</pre>'

 msg.attach(MIMEText(body_template.format(text_color, text, '\n'.join(warnings)), 'html', 'utf-8'))

 if attachments:
 for attachment in attachments:
 msg.attach(attachment)

 smtp = smtplib.SMTP()
 smtp.connect(mail_server)
 if username is not None and password is not None:
 smtp.login(username, password)
 smtp.sendmail(send_from, send_to_list, msg.as_string())
 smtp.close()

 return True