I use Rails 3 + Postmark-Rails. At first, I created account on postmarkapp.com to

Question

Editorial Team

Asked: June 2, 20262026-06-02T00:20:00+00:00 2026-06-02T00:20:00+00:00

I use Rails 3 + Postmark-Rails.

At first, I created account on postmarkapp.com to get my api key.

I Activated my signature by email link [for example, “vitalyp@dot.com”]

— After that, I added this to application.rb

config.action_mailer.delivery_method   = :postmark
config.action_mailer.postmark_settings = { :api_key => "fdcb..." }

I use this method to send emails:

class UserMailer < ActionMailer::Base
  default :from => "vitalyp@dot.com"

  def do_my_mail(to, subj)
    mail(:to => to, :subject => subj)
  end

I get this error:

Postmark::InvalidMessageError
Sender signature not defined for From address.

Any ideas?

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Editorial Team · Answer 1 · 2026-06-02T00:20:01+00:00

Editorial Team

SPF and DKIM are recommended, not required. However, sender signature is required (as stated in the documentation).

Are you sure you are using the same From address as the one used to create the sender signature? This can happen if you are using different email.

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