Error injecting @nestjs-modules/mailer MailerService when publishing a package

Question

I was using @nestjs-modules/mailer in my NestJS API to send emails. As a part of abstraction, common functions and services that are being used by multiple APIs are abstracted out and published as libraries in GitHub.

While doing the same with @nestjs-modules/mailer I am getting this error.

Error setting up transport: Cannot read properties of undefined (reading 'addTransporter')

Here is my module:

@Module({})
export class EmailModule {
  static forRoot(options: EmailModuleOptions): DynamicModule {
    const emailOptionsProvider: Provider = {
      provide: 'EMAIL_MODULE_OPTIONS',
      useValue: options,
    };

    return {
      module: EmailModule,
      imports: [
        MailerModule.forRoot({
          transport: 'smtps://user@domain.com:pass@smtp.domain.com',
          template: {
            dir: path.join(__dirname, 'templates'),
            adapter: new HandlebarsAdapter(),
            options: {
              strict: true,
            },
          },
        }),
      ],
      providers: [emailOptionsProvider, EmailService],
      exports: [EmailService],
      global: true,
    };
  }
}

Here is my service:

@Injectable()
export class EmailService {
  email;
  emailPassword;
  constructor(
    @Inject('EMAIL_MODULE_OPTIONS') private options: EmailModuleOptions,
    private readonly mailerService: MailerService,
  ) {
    this.email = options.adminEmail;
    this.emailPassword = options.adminEmailPassword;
  }

  async sendEmail(action, to, subject, context) {
    context.year = new Date().getFullYear();
    const from = this.email;

    try {
      await this.setAdminTransport();
      await this.mailerService.sendMail({
        transporterName: 'zoho',
        to,
        from,
        subject,
        template: action,
        context,
      });
    } catch (error) {
      console.error('Error sending mail:', error.message);
    }
  }

  private async setAdminTransport(): Promise<void> {
    try {
      const config: Options = {
        host: 'smtp.zoho.com.au',
        port: 465,
        secure: true,
        auth: {
          user: this.email,
          pass: this.emailPassword,
        },
      };
      this.mailerService.addTransporter('zoho', config); // here is the error.
    } catch (error) {
      console.error('Error setting up transport:', error.message);
      throw error;
    }
  }
}

I am not providing the transport in the Module as I have multiple transports and I need them to be set accordingly (I have removed that code from above).

The above code is published as a package in GitHub and is being used in my API.

In my API, I am importing this module in app.module to provide the email address and password and then injecting the new EmailService to call sendEmail

The MailerService is not being injected. How can I inject that?